AVR or ATmega32 Addressing modes and Instruction set description .pdf

1
Instruction Set Nomenclature
Status Register (SREG)
SREG: Status register
C: Carry flag
Z: Zero flag
N: Negative flag
V: Two’s complement overflow indicator
S: N ⊕ V, For signed tests
H: Half Carry flag
T: Transfer bit used by BLD and BST instructions
I: Global interrupt enable/disable flag
Registers and Operands
Rd: Destination (and source) register in the register file
Rr: Source register in the register file
R: Result after instruction is executed
K: Constant data
k: Constant address
b: Bit in the register file or I/O register (3-bit)
s: Bit in the status register (3-bit)
X,Y,Z: Indirect address register
(X=R27:R26, Y=R29:R28 and Z=R31:R30)
A: I/O location address
q: Displacement for direct addressing (6-bit)
Rex. 0856C-09/01
Instruction Set

2 AVR Instruction Set
0856C–09/01
I/O Registers
RAMPX, RAMPY, RAMPZ
Registers concatenated with the X, Y and Z registers enabling indirect addressing of the whole data space on MCUs with
more than 64K bytes data space, and constant data fetch on MCUs with more than 64K bytes program space.
RAMPD
Register concatenated with the Z register enabling direct addressing of the whole data space on MCUs with more than 64K
bytes data space.
EIND
Register concatenated with the instruction word enabling indirect jump and call to the whole program space on MCUs with
more than 64K bytes program space.
Stack
STACK: Stack for return address and pushed registers
SP: Stack Pointer to STACK
Flags
⇔: Flag affected by instruction
0: Flag cleared by instruction
1: Flag set by instruction
-: Flag not affected by instruction

3
AVR Instruction Set
0856C–09/01
The Program and Data Addressing Modes
The AVR Enhanced RISC microcontroller supports powerful and efficient addressing modes for access to the program
memory (Flash) and data memory (SRAM, Register file, I/O Memory, and Extended I/O Memory). This section describes
the various addressing modes supported by the AVR architecture. In the following figures, OP means the operation code
part of the instruction word. To simplify, not all figures show the exact location of the addressing bits. To generalize, the
abstract terms RAMEND and FLASHEND have been used to represent the highest location in data and program space,
respectively.
Note: Not all addressing modes are present in all devices. Refer to the device spesific instruction summary.
Register Direct, Single Register Rd
Figure 1. Direct Single Register Addressing
The operand is contained in register d (Rd).
Register Direct, Two Registers Rd and Rr
Figure 2. Direct Register Addressing, Two Registers
Operands are contained in register r (Rr) and d (Rd). The result is stored in register d (Rd).

0856C–09/01
I/O Direct
Figure 3. I/O Direct Addressing
Operand address is contained in 6 bits of the instruction word. n is the destination or source register address.
Note: Some complex AVR Microcontrollers have more peripheral units than can be supported within the 64 locations reserved in the
opcode for I/O direct addressing. The extended I/O memory from address 64 to 255 can only be reached by data addressing,
not I/O addressing.
Data Direct
Figure 4. Direct Data Addressing
A 16-bit Data Address is contained in the 16 LSBs of a two-word instruction. Rd/Rr specify the destination or source
register.
OP Rr/Rd
16
31
15 0
Data Address
0x0000
RAMEND
20 19
Data Space

5
AVR Instruction Set
0856C–09/01
Data Indirect with Displacement
Figure 5. Data Indirect with Displacement
Operand address is the result of the Y- or Z-register contents added to the address contained in 6 bits of the instruction
word. Rd/Rr specify the destination or source register.
Data Indirect
Figure 6. Data Indirect Addressing
Operand address is the contents of the X-, Y-, or the Z-register. In AVR devices without SRAM, Data Indirect Addressing is
called Register Indirect Addressing. Register Indirect Addressing is a subset of Data Indirect Addressing since the data
space form 0 to 31 is the register file.
Data Space
0x0000
RAMEND
Y OR Z - REGISTER
OP q
Rr/Rd
0
0
5
6
10
15
15
Data Space
0x0000
X, Y OR Z - REGISTER
0
15
RAMEND

0856C–09/01
Data Indirect with Pre-decrement
Figure 7. Data Indirect Addressing with Pre-decrement
The X,- Y-, or the Z-register is decremented before the operation. Operand address is the decremented contents of the X-,
Y-, or the Z-register.
Data Indirect with Post-increment
Figure 8. Data Indirect Addressing with Post-increment
The X-, Y-, or the Z-register is incremented after the operation. Operand address is the content of the X-, Y-, or the Z-regis-
ter prior to incrementing.
Data Space
0x0000
0
15
-1
RAMEND
Data Space
0x0000
0
15
1
RAMEND

7
AVR Instruction Set
0856C–09/01
Program Memory Constant Addressing using the LPM, ELPM, and SPM Instructions
Figure 9. Program Memory Constant Addressing
Constant byte address is specified by the Z-register contents. The 15 MSBs select word address. For LPM, the LSB selects
low byte if cleared (LSB = 0) or high byte if set (LSB = 1). For SPM, the LSB should be cleared. If ELPM is used, the
RAMPZ register is used to extend the Z-register.
Program Memory with Post-increment using the LPM Z+ and ELPM Z+ Instruction
Figure 10. Program Memory Addressing with Post-increment
Constant byte address is specified by the Z-register contents. The 15 MSBs select word address. The LSB selects low byte
if cleared (LSB = 0) or high byte if set (LSB = 1). If ELPM Z+ is used, the RAMPZ register is used to extend the Z-register.
FLASHEND
0x0000
LSB
FLASHEND
0x0000
1
LSB

0856C–09/01
Direct Program Addressing, JMP and CALL
Figure 11. Direct Program Memory Addressing
Program execution continues at the address immediate in the instruction word.
Indirect Program Addressing, IJMP and ICALL
Figure 12. Indirect Program Memory Addressing
Program execution continues at address contained by the Z-register (i.e., the PC is loaded with the contents of the Z-
register).
FLASHEND
31 16
OP 6 MSB
16 LSB
PC
21 0
15 0
0x0000
FLASHEND
PC
15 0
0x0000

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AVR Instruction Set
0856C–09/01
Relative Program Addressing, RJMP and RCALL
Figure 13. Relative Program Memory Addressing
Program execution continues at address PC + k + 1. The relative address k is from -2048 to 2047.
FLASHEND
1
0x0000

0856C–09/01
Conditional Branch Summary
Note: 1. Interchange Rd and Rr in the operation before the test, i.e., CP Rd,Rr → CP Rr,Rd
Test Boolean Mnemonic Complementary Boolean Mnemonic Comment
Rd > Rr Z•(N ⊕ V) = 0 BRLT(1)
Rd ≤ Rr Z+(N ⊕ V) = 1 BRGE* Signed
Rd ≥ Rr (N ⊕ V) = 0 BRGE Rd < Rr (N ⊕ V) = 1 BRLT Signed
Rd = Rr Z = 1 BREQ Rd ≠ Rr Z = 0 BRNE Signed
Rd ≤ Rr Z+(N ⊕ V) = 1 BRGE(1)
Rd > Rr Z•(N ⊕ V) = 0 BRLT* Signed
Rd < Rr (N ⊕ V) = 1 BRLT Rd ≥ Rr (N ⊕ V) = 0 BRGE Signed
Rd > Rr C + Z = 0 BRLO(1)
Rd ≤ Rr C + Z = 1 BRSH* Unsigned
Rd ≥ Rr C = 0 BRSH/BRCC Rd < Rr C = 1 BRLO/BRCS Unsigned
Rd = Rr Z = 1 BREQ Rd ≠ Rr Z = 0 BRNE Unsigned
Rd ≤ Rr C + Z = 1 BRSH(1)
Rd > Rr C + Z = 0 BRLO* Unsigned
Rd < Rr C = 1 BRLO/BRCS Rd ≥ Rr C = 0 BRSH/BRCC Unsigned
Carry C = 1 BRCS No carry C = 0 BRCC Simple
Negative N = 1 BRMI Positive N = 0 BRPL Simple
Overflow V = 1 BRVS No overflow V = 0 BRVC Simple
Zero Z = 1 BREQ Not zero Z = 0 BRNE Simple

11
AVR Instruction Set
0856C–09/01
Complete Instruction Set Summary
Instruction Set Summary
Mnemonics Operands Description Operation Flags
#Clock
Note
Arithmetic and Logic Instructions
ADD Rd, Rr Add without Carry Rd ← Rd + Rr Z,C,N,V,S,H 1
ADC Rd, Rr Add with Carry Rd ← Rd + Rr + C Z,C,N,V,S,H 1
ADIW Rd, K Add Immediate to Word Rd+1:Rd ← Rd+1:Rd + K Z,C,N,V,S 2 (1)
SUB Rd, Rr Subtract without Carry Rd ← Rd - Rr Z,C,N,V,S,H 1
SUBI Rd, K Subtract Immediate Rd ← Rd - K Z,C,N,V,S,H 1
SBC Rd, Rr Subtract with Carry Rd ← Rd - Rr - C Z,C,N,V,S,H 1
SBCI Rd, K Subtract Immediate with Carry Rd ← Rd - K - C Z,C,N,V,S,H 1
SBIW Rd, K Subtract Immediate from Word Rd+1:Rd ← Rd+1:Rd - K Z,C,N,V,S 2 (1)
AND Rd, Rr Logical AND Rd ← Rd • Rr Z,N,V,S 1
ANDI Rd, K Logical AND with Immediate Rd ← Rd • K Z,N,V,S 1
OR Rd, Rr Logical OR Rd ← Rd v Rr Z,N,V,S 1
ORI Rd, K Logical OR with Immediate Rd ← Rd v K Z,N,V,S 1
EOR Rd, Rr Exclusive OR Rd ← Rd ⊕ Rr Z,N,V,S 1
COM Rd One’s Complement Rd ← $FF - Rd Z,C,N,V,S 1
NEG Rd Two’s Complement Rd ← $00 - Rd Z,C,N,V,S,H 1
SBR Rd,K Set Bit(s) in Register Rd ← Rd v K Z,N,V,S 1
CBR Rd,K Clear Bit(s) in Register Rd ← Rd • ($FFh - K) Z,N,V,S 1
INC Rd Increment Rd ← Rd + 1 Z,N,V,S 1
DEC Rd Decrement Rd ← Rd - 1 Z,N,V,S 1
TST Rd Test for Zero or Minus Rd ← Rd • Rd Z,N,V,S 1
CLR Rd Clear Register Rd ← Rd ⊕ Rd Z,N,V,S 1
SER Rd Set Register Rd ← $FF None 1
MUL Rd,Rr Multiply Unsigned R1:R0 ← Rd × Rr (UU) Z,C 2 (1)
MULS Rd,Rr Multiply Signed R1:R0 ← Rd × Rr (SS) Z,C 2 (1)
MULSU Rd,Rr Multiply Signed with Unsigned R1:R0 ← Rd × Rr (SU) Z,C 2 (1)
FMUL Rd,Rr Fractional Multiply Unsigned R1:R0 ← (Rd × Rr)<<1 (UU) Z,C 2 (1)
FMULS Rd,Rr Fractional Multiply Signed R1:R0 ← (Rd × Rr)<<1 (SS) Z,C 2 (1)
FMULSU Rd,Rr Fractional Multiply Signed with
Unsigned
R1:R0 ← (Rd × Rr)<<1 (SU) Z,C 2 (1)
Branch Instructions
RJMP k Relative Jump PC ← PC + k + 1 None 2
IJMP Indirect Jump to (Z) PC(15:0) ← Z, PC(21:16) ← 0 None 2 (1)

0856C–09/01
EIJMP Extended Indirect Jump to (Z) PC(15:0) ← Z, PC(21:16) ← EIND None 2 (1)
JMP k Jump PC ← k None 3 (1)
RCALL k Relative Call Subroutine PC ← PC + k + 1 None 3 / 4 (4)
ICALL Indirect Call to (Z) PC(15:0) ← Z, PC(21:16) ← 0 None 3 / 4 (1)(4)
EICALL Extended Indirect Call to (Z) PC(15:0) ← Z, PC(21:16) ← EIND None 4 (1)(4)
CALL k Call Subroutine PC ← k None 4 / 5 (1)(4)
RET Subroutine Return PC ← STACK None 4 / 5 (4)
RETI Interrupt Return PC ← STACK I 4 / 5 (4)
CPSE Rd,Rr Compare, Skip if Equal if (Rd = Rr) PC ← PC + 2 or 3 None 1 / 2 / 3
CP Rd,Rr Compare Rd - Rr Z,C,N,V,S,H 1
CPC Rd,Rr Compare with Carry Rd - Rr - C Z,C,N,V,S,H 1
CPI Rd,K Compare with Immediate Rd - K Z,C,N,V,S,H 1
SBRC Rr, b Skip if Bit in Register Cleared if (Rr(b)=0) PC ← PC + 2 or 3 None 1 / 2 / 3
SBRS Rr, b Skip if Bit in Register Set if (Rr(b)=1) PC ← PC + 2 or 3 None 1 / 2 / 3
SBIC A, b Skip if Bit in I/O Register Cleared if(I/O(A,b)=0) PC ← PC + 2 or 3 None 1 / 2 / 3
SBIS A, b Skip if Bit in I/O Register Set If(I/O(A,b)=1) PC ← PC + 2 or 3 None 1 / 2 / 3
BRBS s, k Branch if Status Flag Set if (SREG(s) = 1) then PC ←PC+k + 1 None 1 / 2
BRBC s, k Branch if Status Flag Cleared if (SREG(s) = 0) then PC ←PC+k + 1 None 1 / 2
BREQ k Branch if Equal if (Z = 1) then PC ← PC + k + 1 None 1 / 2
BRNE k Branch if Not Equal if (Z = 0) then PC ← PC + k + 1 None 1 / 2
BRCS k Branch if Carry Set if (C = 1) then PC ← PC + k + 1 None 1 / 2
BRCC k Branch if Carry Cleared if (C = 0) then PC ← PC + k + 1 None 1 / 2
BRSH k Branch if Same or Higher if (C = 0) then PC ← PC + k + 1 None 1 / 2
BRLO k Branch if Lower if (C = 1) then PC ← PC + k + 1 None 1 / 2
BRMI k Branch if Minus if (N = 1) then PC ← PC + k + 1 None 1 / 2
BRPL k Branch if Plus if (N = 0) then PC ← PC + k + 1 None 1 / 2
BRGE k Branch if Greater or Equal, Signed if (N ⊕ V= 0) then PC ← PC + k + 1 None 1 / 2
BRLT k Branch if Less Than, Signed if (N ⊕ V= 1) then PC ← PC + k + 1 None 1 / 2
BRHS k Branch if Half Carry Flag Set if (H = 1) then PC ← PC + k + 1 None 1 / 2
BRHC k Branch if Half Carry Flag Cleared if (H = 0) then PC ← PC + k + 1 None 1 / 2
BRTS k Branch if T Flag Set if (T = 1) then PC ← PC + k + 1 None 1 / 2
BRTC k Branch if T Flag Cleared if (T = 0) then PC ← PC + k + 1 None 1 / 2
BRVS k Branch if Overflow Flag is Set if (V = 1) then PC ← PC + k + 1 None 1 / 2
BRVC k Branch if Overflow Flag is Cleared if (V = 0) then PC ← PC + k + 1 None 1 / 2
BRIE k Branch if Interrupt Enabled if ( I = 1) then PC ← PC + k + 1 None 1 / 2
Instruction Set Summary (Continued)
#Clock
Note

13
AVR Instruction Set
0856C–09/01
BRID k Branch if Interrupt Disabled if ( I = 0) then PC ← PC + k + 1 None 1 / 2
Data Transfer Instructions
MOV Rd, Rr Copy Register Rd ← Rr None 1
MOVW Rd, Rr Copy Register Pair Rd+1:Rd ← Rr+1:Rr None 1 (1)
LDI Rd, K Load Immediate Rd ← K None 1
LDS Rd, k Load Direct from data space Rd ← (k) None 2 (1)(4)
LD Rd, X Load Indirect Rd ← (X) None 2 (2)(4)
LD Rd, X+ Load Indirect and Post-Increment Rd ← (X), X ← X + 1 None 2 (2)(4)
LD Rd, -X Load Indirect and Pre-Decrement X ← X - 1, Rd ← (X) None 2 (2)(4)
LD Rd, Y Load Indirect Rd ← (Y) None 2 (2)(4)
LD Rd, Y+ Load Indirect and Post-Increment Rd ← (Y), Y ← Y + 1 None 2 (2)(4)
LD Rd, -Y Load Indirect and Pre-Decrement Y ← Y - 1, Rd ← (Y) None 2 (2)(4)
LDD Rd,Y+q Load Indirect with Displacement Rd ← (Y + q) None 2 (1)(4)
LD Rd, Z Load Indirect Rd ← (Z) None 2 (2)(4)
LD Rd, Z+ Load Indirect and Post-Increment Rd ← (Z), Z ← Z+1 None 2 (2)(4)
LD Rd, -Z Load Indirect and Pre-Decrement Z ← Z - 1, Rd ← (Z) None 2 (2)(4)
LDD Rd, Z+q Load Indirect with Displacement Rd ← (Z + q) None 2 (1)(4)
STS k, Rr Store Direct to data space (k) ← Rd None 2 (1)(4)
ST X, Rr Store Indirect (X) ← Rr None 2 (2)(4)
ST X+, Rr Store Indirect and Post-Increment (X) ← Rr, X ← X + 1 None 2 (2)(4)
ST -X, Rr Store Indirect and Pre-Decrement X ← X - 1, (X) ← Rr None 2 (2)(4)
ST Y, Rr Store Indirect (Y) ← Rr None 2 (2)(4)
ST Y+, Rr Store Indirect and Post-Increment (Y) ← Rr, Y ← Y + 1 None 2 (2)(4)
ST -Y, Rr Store Indirect and Pre-Decrement Y ← Y - 1, (Y) ← Rr None 2 (2)(4)
STD Y+q,Rr Store Indirect with Displacement (Y + q) ← Rr None 2 (1)(4)
ST Z, Rr Store Indirect (Z) ← Rr None 2 (2)(4)
ST Z+, Rr Store Indirect and Post-Increment (Z) ← Rr, Z ← Z + 1 None 2 (2)(4)
ST -Z, Rr Store Indirect and Pre-Decrement Z ← Z - 1, (Z) ← Rr None 2 (2)(4)
STD Z+q,Rr Store Indirect with Displacement (Z + q) ← Rr None 2 (1)(4)
LPM Load Program Memory R0 ← (Z) None 3 (3)
LPM Rd, Z Load Program Memory Rd ← (Z) None 3 (3)
LPM Rd, Z+ Load Program Memory and Post-
Increment
Rd ← (Z), Z ← Z + 1 None 3 (3)
ELPM Extended Load Program Memory R0 ← (RAMPZ:Z) None 3 (1)
ELPM Rd, Z Extended Load Program Memory Rd ← (RAMPZ:Z) None 3 (1)
#Clock
Note

0856C–09/01
ELPM Rd, Z+ Extended Load Program Memory
and Post-Increment
Rd ← (RAMPZ:Z), Z ← Z + 1 None 3 (1)
SPM Store Program Memory (Z) ← R1:R0 None - (1)
IN Rd, A In From I/O Location Rd ← I/O(A) None 1
OUT A, Rr Out To I/O Location I/O(A) ← Rr None 1
PUSH Rr Push Register on Stack STACK ← Rr None 2 (1)
POP Rd Pop Register from Stack Rd ← STACK None 2 (1)
Bit and Bit-test Instructions
LSL Rd Logical Shift Left Rd(n+1)←Rd(n),Rd(0)←0,C←Rd(7) Z,C,N,V,H 1
LSR Rd Logical Shift Right Rd(n)←Rd(n+1),Rd(7)←0,C←Rd(0) Z,C,N,V 1
ROL Rd Rotate Left Through Carry Rd(0)←C,Rd(n+1)←Rd(n),C←Rd(7) Z,C,N,V,H 1
ROR Rd Rotate Right Through Carry Rd(7)←C,Rd(n)←Rd(n+1),C←Rd(0) Z,C,N,V 1
ASR Rd Arithmetic Shift Right Rd(n) ← Rd(n+1), n=0..6 Z,C,N,V 1
SWAP Rd Swap Nibbles Rd(3..0) ↔ Rd(7..4) None 1
BSET s Flag Set SREG(s) ← 1 SREG(s) 1
BCLR s Flag Clear SREG(s) ← 0 SREG(s) 1
SBI A, b Set Bit in I/O Register I/O(A, b) ← 1 None 2
CBI A, b Clear Bit in I/O Register I/O(A, b) ← 0 None 2
BST Rr, b Bit Store from Register to T T ← Rr(b) T 1
BLD Rd, b Bit load from T to Register Rd(b) ← T None 1
SEC Set Carry C ← 1 C 1
CLC Clear Carry C ← 0 C 1
SEN Set Negative Flag N ← 1 N 1
CLN Clear Negative Flag N ← 0 N 1
SEZ Set Zero Flag Z ← 1 Z 1
CLZ Clear Zero Flag Z ← 0 Z 1
SEI Global Interrupt Enable I ← 1 I 1
CLI Global Interrupt Disable I ← 0 I 1
SES Set Signed Test Flag S ← 1 S 1
CLS Clear Signed Test Flag S ← 0 S 1
SEV Set Two’s Complement Overflow V ← 1 V 1
CLV Clear Two’s Complement Overflow V ← 0 V 1
SET Set T in SREG T ← 1 T 1
CLT Clear T in SREG T ← 0 T 1
SEH Set Half Carry Flag in SREG H ← 1 H 1
CLH Clear Half Carry Flag in SREG H ← 0 H 1
#Clock
Note

15
AVR Instruction Set
0856C–09/01
Notes: 1. This instruction is not available in all devices. Refer to the device specific instruction set summary.
2. Not all variants of this instruction are available in all devices. Refer to the device specific instruction set summary.
3. Not all variants of the LPM instruction are available in all devices. Refer to the device specific instruction set summary. The
LPM instruction is not implemented at all in the AT90S1200 device.
4. Cycle times for data memory accesses assume internal memory accesses, and are not valid for accesses via the external
RAM interface. For LD, ST, LDS, STS, PUSH, POP, add one cycle plus one cycle for each wait state. For CALL, ICALL,
EICALL, RCALL, RET, RETI in devices with 16-bit PC, add three cycles plus two cycles for each wait state. For CALL,
ICALL, EICALL, RCALL, RET, RETI in devices with 22-bit PC, add five cycles plus three cycles for each wait state.
MCU Control Instructions
BREAK Break (See specific descr. for BREAK) None 1 (1)
NOP No Operation None 1
SLEEP Sleep (see specific descr. for Sleep) None 1
WDR Watchdog Reset (see specific descr. for WDR) None 1
#Clock
Note

0856C–09/01
ADC – Add with Carry
Description:
Adds two registers and the contents of the C flag and places the result in the destination register Rd.
Operation:
(i) Rd ← Rd + Rr + C
Syntax: Operands: Program Counter:
(i) ADC Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
Status Register (SREG) Boolean Formula:
H: Rd3•Rr3+Rr3•R3+R3•Rd3
Set if there was a carry from bit 3; cleared otherwise
S: N ⊕ V, For signed tests.
V: Rd7•Rr7•R7+Rd7•Rr7•R7
Set if two’s complement overflow resulted from the operation; cleared otherwise.
N: R7
Set if MSB of the result is set; cleared otherwise.
Z: R7• R6 •R5• R4 •R3 •R2 •R1 •R0
Set if the result is $00; cleared otherwise.
C: Rd7•Rr7+Rr7•R7+R7•Rd7
Set if there was carry from the MSB of the result; cleared otherwise.
R (Result) equals Rd after the operation.
Example:
; Add R1:R0 to R3:R2
add r2,r0 ; Add low byte
adc r3,r1 ; Add with carry high byte
Words: 1 (2 bytes)
Cycles: 1
0001 11rd dddd rrrr
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

17
AVR Instruction Set
0856C–09/01
ADD – Add without Carry
Description:
Adds two registers without the C flag and places the result in the destination register Rd.
Operation:
(i) Rd ← Rd + Rr
(i) ADD Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
Status Register (SREG) and Boolean Formula:
H: Rd3•Rr3+Rr3•R3+R3•Rd3
Set if there was a carry from bit 3; cleared otherwise
V: Rd7•Rr7•R7+Rd7•Rr7•R7
N: R7
Z: R7• R6 •R5• R4 •R3 •R2 •R1 •R0
C: Rd7 •Rr7 +Rr7 •R7+ R7 •Rd7
Example:
add r1,r2 ; Add r2 to r1 (r1=r1+r2)
add r28,r28 ; Add r28 to itself (r28=r28+r28)
Words: 1 (2 bytes)
Cycles: 1
0000 11rd dddd rrrr
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

0856C–09/01
ADIW – Add Immediate to Word
Description:
Adds an immediate value (0 - 63) to a register pair and places the result in the register pair. This instruction operates on the
upper four register pairs, and is well suited for operations on the pointer registers.
This instruction is not available in all devices. Refer to the device specific instruction set summary.
Operation:
(i) Rd+1:Rd ← Rd+1:Rd + K
(i) ADIW Rd+1:Rd,K d ∈ {24,26,28,30}, 0 ≤ K ≤ 63 PC ← PC + 1
16-bit Opcode:
V: Rdh7 •=R15
N: R15
Z: R15 •R14 •R13 •R12 •R11 •R10 •R9 •R8 •R7• R6• R5• R4• R3• R2 •R1• R0
C: R15 • Rdh7
R (Result) equals Rdh:Rdl after the operation (Rdh7-Rdh0 = R15-R8, Rdl7-Rdl0=R7-R0).
Example:
adiw r25:24,1 ; Add 1 to r25:r24
adiw ZH:ZL,63 ; Add 63 to the Z pointer(r31:r30)
Words: 1 (2 bytes)
Cycles: 2
1001 0110 KKdd KKKK
I T H S V N Z C
– – – ⇔ ⇔ ⇔ ⇔ ⇔

19
AVR Instruction Set
0856C–09/01
AND – Logical AND
Description:
Performs the logical AND between the contents of register Rd and register Rr and places the result in the destination regis-
ter Rd.
Operation:
(i) Rd ← Rd • Rr
(i) AND Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
V: 0
Cleared
N: R7
Z: R7 •R6 •R5 •R4 •R3• R2 •R1 •R0
Example:
and r2,r3 ; Bitwise and r2 and r3, result in r2
ldi r16,1 ; Set bitmask 0000 0001 in r16
and r2,r16 ; Isolate bit 0 in r2
Words: 1 (2 bytes)
Cycles: 1
0010 00rd dddd rrrr
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ –

0856C–09/01
ANDI – Logical AND with Immediate
Description:
Performs the logical AND between the contents of register Rd and a constant and places the result in the destination regis-
ter Rd.
Operation:
(i) Rd ← Rd • K
(i) ANDI Rd,K 16 ≤ d ≤ 31, 0 ≤ K ≤ 255 PC ← PC + 1
16-bit Opcode:
V: 0
Cleared
N: R7
Z: R7 •R6• R5•R4 •R3• R2• R1• R0
Example:
andi r17,$0F ; Clear upper nibble of r17
andi r18,$10 ; Isolate bit 4 in r18
andi r19,$AA ; Clear odd bits of r19
Words: 1 (2 bytes)
Cycles: 1
0111 KKKK dddd KKKK
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ –

21
AVR Instruction Set
0856C–09/01
ASR – Arithmetic Shift Right
Description:
Shifts all bits in Rd one place to the right. Bit 7 is held constant. Bit 0 is loaded into the C flag of the SREG. This operation
effectively divides a signed value by two without changing its sign. The carry flag can be used to round the result.
Operation:
(i)
(i) ASR Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
V: N ⊕ C (For N and C after the shift)
N: R7
Z: R7 •R6 •R5• R4 •R3 •R2• R1• R0
C: Rd0
Set if, before the shift, the LSB of Rd was set; cleared otherwise.
Example:
ldi r16,$10 ; Load decimal 16 into r16
asr r16 ; r16=r16 / 2
ldi r17,$FC ; Load -4 in r17
asr r17 ; r17=r17/2
Words: 1 (2 bytes)
Cycles: 1
1001 010d dddd 0101
I T H S V N Z C
– – – ⇔ ⇔ ⇔ ⇔ ⇔
b7-------------------b0 C

0856C–09/01
BCLR – Bit Clear in SREG
Description:
Clears a single flag in SREG.
Operation:
(i) SREG(s) ← 0
(i) BCLR s 0 ≤ s ≤ 7 PC ← PC + 1
16-bit Opcode:
I: 0 if s = 7; Unchanged otherwise.
T: 0 if s = 6; Unchanged otherwise.
H: 0 if s = 5; Unchanged otherwise.
S: 0 if s = 4; Unchanged otherwise.
V: 0 if s = 3; Unchanged otherwise.
N: 0 if s = 2; Unchanged otherwise.
Z: 0 if s = 1; Unchanged otherwise.
C: 0 if s = 0; Unchanged otherwise.
Example:
bclr 0 ; Clear carry flag
bclr 7 ; Disable interrupts
Words: 1 (2 bytes)
Cycles: 1
1001 0100 1sss 1000
I T H S V N Z C
⇔ ⇔ ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

23
AVR Instruction Set
0856C–09/01
BLD – Bit Load from the T Flag in SREG to a Bit in Register
Description:
Copies the T flag in the SREG (status register) to bit b in register Rd.
Operation:
(i) Rd(b) ← T
(i) BLD Rd,b 0 ≤ d ≤ 31, 0 ≤ b ≤ 7 PC ← PC + 1
16 bit Opcode:
Example:
; Copy bit
bst r1,2 ; Store bit 2 of r1 in T flag
bld r0,4 ; Load T flag into bit 4 of r0
Words: 1 (2 bytes)
Cycles: 1
1111 100d dddd 0bbb
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRBC – Branch if Bit in SREG is Cleared
Description:
Conditional relative branch. Tests a single bit in SREG and branches relatively to PC if the bit is cleared. This instruction
branches relatively to PC in either direction (PC - 63 ≤=destination ≤=PC + 64). The parameter k is the offset from PC and is
represented in two’s complement form.
Operation:
(i) If SREG(s) = 0 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRBC s,k 0 ≤ s ≤ 7, -64 ≤ k ≤ +63 PC ← PC + k + 1
PC ← PC + 1, if condition is false
16-bit Opcode:
Example:
cpi r20,5 ; Compare r20 to the value 5
brbc 1,noteq ; Branch if zero flag cleared
...
noteq:nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1 if condition is false
2 if condition is true
1111 01kk kkkk ksss
I T H S V N Z C
– – – – – – – –

25
AVR Instruction Set
0856C–09/01
BRBS – Branch if Bit in SREG is Set
Description:
Conditional relative branch. Tests a single bit in SREG and branches relatively to PC if the bit is set. This instruction
branches relatively to PC in either direction (PC - 63 ≤=destination=≤=PC + 64). The parameter k is the offset from PC and is
represented in two’s complement form.
Operation:
(i) If SREG(s) = 1 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRBS s,k 0 ≤ s ≤ 7, -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
bst r0,3 ; Load T bit with bit 3 of r0
brbs 6,bitset ; Branch T bit was set
...
bitset: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk ksss
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRCC – Branch if Carry Cleared
Description:
Conditional relative branch. Tests the Carry flag (C) and branches relatively to PC if C is cleared. This instruction branches
relatively to PC in either direction (PC - 63 ≤=destination ≤=PC + 64). The parameter k is the offset from PC and is repre-
sented in two’s complement form. (Equivalent to instruction BRBC 0,k).
Operation:
(i) If C = 0 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRCC k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
add r22,r23 ; Add r23 to r22
brcc nocarry ; Branch if carry cleared
...
nocarry: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 01kk kkkk k000
I T H S V N Z C
– – – – – – – –

27
AVR Instruction Set
0856C–09/01
BRCS – Branch if Carry Set
Description:
Conditional relative branch. Tests the Carry flag (C) and branches relatively to PC if C is set. This instruction branches rel-
atively to PC in either direction (PC - 63 ≤=destination=≤=PC + 64). The parameter k is the offset from PC and is represented
in two’s complement form. (Equivalent to instruction BRBS 0,k).
Operation:
(i) If C = 1 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRCS k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
cpi r26,$56 ; Compare r26 with $56
brcs carry ; Branch if carry set
...
carry: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk k000
I T H S V N Z C
– – – – – – – –

0856C–09/01
BREAK – Break
Description:
The BREAK instruction is used by the On-chip Debug system, and is normally not used in the application software. When
the BREAK instruction is executed, the AVR CPU is set in the Stopped Mode. This gives the On-chip Debugger access to
internal resources.
If any lock bits are set, or either the JTAGEN or OCDEN fuses are unprogrammed, the CPU will treat the BREAK instruc-
tion as a NOP and will not enter the Stopped mode.
Operation:
(i) On-chip Debug system break.
(i) BREAK None PC ← PC + 1
16-bit Opcode:
Words: 1 (2 bytes)
Cycles: 1
1001 0101 1001 1000
I T H S V N Z C
– – – – – – – –

29
AVR Instruction Set
0856C–09/01
BREQ – Branch if Equal
Description:
Conditional relative branch. Tests the Zero flag (Z) and branches relatively to PC if Z is set. If the instruction is executed
immediately after any of the instructions CP, CPI, SUB or SUBI, the branch will occur if and only if the unsigned or signed
binary number represented in Rd was equal to the unsigned or signed binary number represented in Rr. This instruction
represented in two’s complement form. (Equivalent to instruction BRBS 1,k).
Operation:
(i) If Rd = Rr (Z = 1) then PC ← PC + k + 1, else PC ← PC + 1
(i) BREQ k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
cp r1,r0 ; Compare registers r1 and r0
breq equal ; Branch if registers equal
...
equal: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk k001
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRGE – Branch if Greater or Equal (Signed)
Description:
Conditional relative branch. Tests the Signed flag (S) and branches relatively to PC if S is cleared. If the instruction is exe-
cuted immediately after any of the instructions CP, CPI, SUB or SUBI, the branch will occur if and only if the signed binary
number represented in Rd was greater than or equal to the signed binary number represented in Rr. This instruction
represented in two’s complement form. (Equivalent to instruction BRBC 4,k).
Operation:
(i) If Rd ≥ Rr (N ⊕ V = 0) then PC ← PC + k + 1, else PC ← PC + 1
(i) BRGE k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
cp r11,r12 ; Compare registers r11 and r12
brge greateq ; Branch if r11 ≥ r12 (signed)
...
greateq: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 01kk kkkk k100
I T H S V N Z C
– – – – – – – –

31
AVR Instruction Set
0856C–09/01
BRHC – Branch if Half Carry Flag is Cleared
Description:
Conditional relative branch. Tests the Half Carry flag (H) and branches relatively to PC if H is cleared. This instruction
Operation:
(i) If H = 0 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRHC k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
brhc hclear ; Branch if half carry flag cleared
...
hclear: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 01kk kkkk k101
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRHS – Branch if Half Carry Flag is Set
Description:
Conditional relative branch. Tests the Half Carry flag (H) and branches relatively to PC if H is set. This instruction branches
relatively to PC in either direction (PC - 63 ≤=destination ≤=PC + 64). The parameter k is the offset from PC and is repre-
sented in two’s complement form. (Equivalent to instruction BRBS 5,k).
Operation:
(i) If H = 1 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRHS k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
brhs hset ; Branch if half carry flag set
...
hset: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk k101
I T H S V N Z C
– – – – – – – –

33
AVR Instruction Set
0856C–09/01
BRID – Branch if Global Interrupt is Disabled
Description:
Conditional relative branch. Tests the Global Interrupt flag (I) and branches relatively to PC if I is cleared. This instruction
Operation:
(i) If I = 0 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRID k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
brid intdis ; Branch if interrupt disabled
...
intdis: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 01kk kkkk k111
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRIE – Branch if Global Interrupt is Enabled
Description:
Conditional relative branch. Tests the Global Interrupt flag (I) and branches relatively to PC if I is set. This instruction
represented in two’s complement form. (Equivalent to instruction BRBS 7,k).
Operation:
(i) If I = 1 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRIE k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
brie inten ; Branch if interrupt enabled
...
inten: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk k111
I T H S V N Z C
– – – – – – – –

35
AVR Instruction Set
0856C–09/01
BRLO – Branch if Lower (Unsigned)
Description:
Conditional relative branch. Tests the Carry flag (C) and branches relatively to PC if C is set. If the instruction is executed
immediately after any of the instructions CP, CPI, SUB or SUBI, the branch will occur if and only if the unsigned binary
number represented in Rd was smaller than the unsigned binary number represented in Rr. This instruction branches rela-
tively to PC in either direction (PC - 63 ≤=destination=≤=PC + 64). The parameter k is the offset from PC and is represented
in two’s complement form. (Equivalent to instruction BRBS 0,k).
Operation:
(i) If Rd < Rr (C = 1) then PC ← PC + k + 1, else PC ← PC + 1
(i) BRLO k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
eor r19,r19 ; Clear r19
loop: inc r19 ; Increase r19
...
cpi r19,$10 ; Compare r19 with $10
brlo loop ; Branch if r19 < $10 (unsigned)
nop ; Exit from loop (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk k000
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRLT – Branch if Less Than (Signed)
Description:
Conditional relative branch. Tests the Signed flag (S) and branches relatively to PC if S is set. If the instruction is executed
immediately after any of the instructions CP, CPI, SUB or SUBI, the branch will occur if and only if the signed binary num-
ber represented in Rd was less than the signed binary number represented in Rr. This instruction branches relatively to PC
in either direction (PC - 63 ≤=destination ≤=PC + 64). The parameter k is the offset from PC and is represented in two’s com-
plement form. (Equivalent to instruction BRBS 4,k).
Operation:
(i) If Rd < Rr (N ⊕ V = 1) then PC ← PC + k + 1, else PC ← PC + 1
(i) BRLT k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
cp r16,r1 ; Compare r16 to r1
brlt less ; Branch if r16 < r1 (signed)
...
less: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk k100
I T H S V N Z C
– – – – – – – –

37
AVR Instruction Set
0856C–09/01
BRMI – Branch if Minus
Description:
Conditional relative branch. Tests the Negative flag (N) and branches relatively to PC if N is set. This instruction branches
relatively to PC in either direction (PC - 63 ≤=destination=≤=PC + 64). The parameter k is the offset from PC and is repre-
Operation:
(i) If N = 1 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRMI k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
subi r18,4 ; Subtract 4 from r18
brmi negative ; Branch if result negative
...
negative: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk k010
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRNE – Branch if Not Equal
Description:
Conditional relative branch. Tests the Zero flag (Z) and branches relatively to PC if Z is cleared. If the instruction is exe-
cuted immediately after any of the instructions CP, CPI, SUB or SUBI, the branch will occur if and only if the unsigned or
signed binary number represented in Rd was not equal to the unsigned or signed binary number represented in Rr. This
instruction branches relatively to PC in either direction (PC - 63 ≤=destination=≤=PC + 64). The parameter k is the offset from
PC and is represented in two’s complement form. (Equivalent to instruction BRBC 1,k).
Operation:
(i) If Rd ≠ Rr (Z = 0) then PC ← PC + k + 1, else PC ← PC + 1
(i) BRNE k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
loop: inc r27 ; Increase r27
...
cpi r27,5 ; Compare r27 to 5
brne loop ; Branch if r27<>5
nop ; Loop exit (do nothing)
Words: 1 (2 bytes)
1111 01kk kkkk k001
I T H S V N Z C
– – – – – – – –

39
AVR Instruction Set
0856C–09/01
BRPL – Branch if Plus
Description:
Conditional relative branch. Tests the Negative flag (N) and branches relatively to PC if N is cleared. This instruction
Operation:
(i) If N = 0 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRPL k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
subi r26,$50 ; Subtract $50 from r26
brpl positive ; Branch if r26 positive
...
positive: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 01kk kkkk k010
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRSH – Branch if Same or Higher (Unsigned)
Description:
Conditional relative branch. Tests the Carry flag (C) and branches relatively to PC if C is cleared. If the instruction is exe-
cuted immediately after execution of any of the instructions CP, CPI, SUB or SUBI the branch will occur if and only if the
unsigned binary number represented in Rd was greater than or equal to the unsigned binary number represented in Rr.
This instruction branches relatively to PC in either direction (PC - 63 ≤=destination ≤=PC + 64). The parameter k is the offset
from PC and is represented in two’s complement form. (Equivalent to instruction BRBC 0,k).
Operation:
(i) If Rd ≥Rr (C = 0) then PC ← PC + k + 1, else PC ← PC + 1
(i) BRSH k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
subi r19,4 ; Subtract 4 from r19
brsh highsm ; Branch if r19 >= 4 (unsigned)
...
highsm: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 01kk kkkk k000
I T H S V N Z C
– – – – – – – –

41
AVR Instruction Set
0856C–09/01
BRTC – Branch if the T Flag is Cleared
Description:
Conditional relative branch. Tests the T flag and branches relatively to PC if T is cleared. This instruction branches rela-
tively to PC in either direction (PC - 63 ≤=destination ≤=PC + 64). The parameter k is the offset from PC and is represented
in two’s complement form. (Equivalent to instruction BRBC 6,k).
Operation:
(i) If T = 0 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRTC k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
brtc tclear ; Branch if this bit was cleared
...
tclear: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 01kk kkkk k110
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRTS – Branch if the T Flag is Set
Description:
Conditional relative branch. Tests the T flag and branches relatively to PC if T is set. This instruction branches relatively to
PC in either direction (PC - 63 ≤=destination ≤=PC + 64). The parameter k is the offset from PC and is represented in two’s
complement form. (Equivalent to instruction BRBS 6,k).
Operation:
(i) If T = 1 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRTS k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
brts tset ; Branch if this bit was set
...
tset: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk k110
I T H S V N Z C
– – – – – – – –

43
AVR Instruction Set
0856C–09/01
BRVC – Branch if Overflow Cleared
Description:
Conditional relative branch. Tests the Overflow flag (V) and branches relatively to PC if V is cleared. This instruction branch-
es relatively to PC in either direction (PC - 63 ≤=destination=≤=PC + 64). The parameter k is the offset from PC and is repre-
sented in two’s complement form. (Equivalent to instruction BRBC 3,k).
Operation:
(i) If V = 0 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRVC k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
brvc noover ; Branch if no overflow
...
noover: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 01kk kkkk k011
I T H S V N Z C
– – – – – – – –

0856C–09/01
BRVS – Branch if Overflow Set
Description:
Conditional relative branch. Tests the Overflow flag (V) and branches relatively to PC if V is set. This instruction branches
relatively to PC in either direction (PC - 63 ≤=destination=≤=PC + 64). The parameter k is the offset from PC and is repre-
Operation:
(i) If V = 1 then PC ← PC + k + 1, else PC ← PC + 1
(i) BRVS k -64 ≤ k ≤ +63 PC ← PC + k + 1
16-bit Opcode:
Example:
brvs overfl ; Branch if overflow
...
overfl: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
1111 00kk kkkk k011
I T H S V N Z C
– – – – – – – –

45
AVR Instruction Set
0856C–09/01
BSET – Bit Set in SREG
Description:
Sets a single flag or bit in SREG.
Operation:
(i) SREG(s) ← 1
(i) BSET s 0 ≤ s ≤ 7 PC ← PC + 1
16-bit Opcode:
I: 1 if s = 7; Unchanged otherwise.
T: 1 if s = 6; Unchanged otherwise.
H: 1 if s = 5; Unchanged otherwise.
S: 1 if s = 4; Unchanged otherwise.
V: 1 if s = 3; Unchanged otherwise.
N: 1 if s = 2; Unchanged otherwise.
Z: 1 if s = 1; Unchanged otherwise.
C: 1 if s = 0; Unchanged otherwise.
Example:
bset 6 ; Set T flag
bset 7 ; Enable interrupt
Words: 1 (2 bytes)
Cycles: 1
1001 0100 0sss 1000
I T H S V N Z C
⇔ ⇔ ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

0856C–09/01
BST – Bit Store from Bit in Register to T Flag in SREG
Description:
Stores bit b from Rd to the T flag in SREG (status register).
Operation:
(i) T ← Rd(b)
(i) BST Rd,b 0 ≤ d ≤ 31, 0 ≤ b ≤ 7 PC ← PC + 1
16-bit Opcode:
T: 0 if bit b in Rd is cleared. Set to 1 otherwise.
Example:
; Copy bit
bld r0,4 ; Load T into bit 4 of r0
Words: 1 (2 bytes)
Cycles: 1
1111 101d dddd 0bbb
I T H S V N Z C
– ⇔ – – – – – –

47
AVR Instruction Set
0856C–09/01
CALL – Long Call to a Subroutine
Description:
Calls to a subroutine within the entire program memory. The return address (to the instruction after the CALL) will be stored
onto the stack. (See also RCALL). The stack pointer uses a post-decrement scheme during CALL.
Operation:
(i) PC ← k Devices with 16 bits PC, 128K bytes program memory maximum.
(ii) PC ← k Devices with 22 bits PC, 8M bytes program memory maximum.
Syntax: Operands: Program Counter Stack:
(i) CALL k 0 ≤ k < 64K PC ← k STACK ← PC+2
SP ← SP-2, (2 bytes, 16 bits)
(ii) CALL k 0 ≤ k < 4M PC ← k STACK ← PC+2
SP ← SP-3 (3 bytes, 22 bits)
32-bit Opcode:
Example:
mov r16,r0 ; Copy r0 to r16
call check ; Call subroutine
nop ; Continue (do nothing)
...
check: cpi r16,$42 ; Check if r16 has a special value
breq error ; Branch if equal
ret ; Return from subroutine
...
error: rjmp error ; Infinite loop
Words: 2 (4 bytes)
Cycles: 4, devices with 16 bit PC
5, devices with 22 bit PC
1001 010k kkkk 111k
kkkk kkkk kkkk kkkk
I T H S V N Z C
– – – – – – – –

0856C–09/01
CBI – Clear Bit in I/O Register
Description:
Clears a specified bit in an I/O register. This instruction operates on the lower 32 I/O registers – addresses 0-31.
Operation:
(i) I/O(A,b) ← 0
(i) CBI A,b 0 ≤ A ≤ 31, 0 ≤ b ≤ 7 PC ← PC + 1
16-bit Opcode:
Example:
cbi $12,7 ; Clear bit 7 in Port D
Words: 1 (2 bytes)
Cycles: 2
1001 1000 AAAA Abbb
I T H S V N Z C
– – – – – – – –

49
AVR Instruction Set
0856C–09/01
CBR – Clear Bits in Register
Description:
Clears the specified bits in register Rd. Performs the logical AND between the contents of register Rd and the complement
of the constant mask K. The result will be placed in register Rd.
Operation:
(i) Rd ← Rd • ($FF - K)
(i) CBR Rd,K 16 ≤ d ≤ 31, 0 ≤ K ≤ 255 PC ← PC + 1
16-bit Opcode: (see ANDI with K complemented)
V: 0
Cleared
N: R7
Z: R7 •R6 •R5• R4• R3 •R2• R1• R0
Example:
cbr r16,$F0 ; Clear upper nibble of r16
cbr r18,1 ; Clear bit 0 in r18
Words: 1 (2 bytes)
Cycles: 1
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ –

0856C–09/01
CLC – Clear Carry Flag
Description:
Clears the Carry flag (C) in SREG (status register).
Operation:
(i) C ← 0
(i) CLC None PC ← PC + 1
16-bit Opcode:
C: 0
Carry flag cleared
Example:
add r0,r0 ; Add r0 to itself
clc ; Clear carry flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 1000 1000
I T H S V N Z C
– – – – – – – 0

51
AVR Instruction Set
0856C–09/01
CLH – Clear Half Carry Flag
Description:
Clears the Half Carry flag (H) in SREG (status register).
Operation:
(i) H ← 0
(i) CLH None PC ← PC + 1
16-bit Opcode:
H: 0
Half Carry flag cleared
Example:
clh ; Clear the Half Carry flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 1101 1000
I T H S V N Z C
– – 0 – – – – –

0856C–09/01
CLI – Clear Global Interrupt Flag
Description:
Clears the Global Interrupt flag (I) in SREG (status register). The interrupts will be immediately disabled. No interrupt will be
executed after the CLI instruction, even if it occurs simultaneously with the CLI instruction.
Operation:
(i) I ← 0
(i) CLI None PC ← PC + 1
16-bit Opcode:
I: 0
Global Interrupt flag cleared
Example:
in temp, SREG ; Store SREG value (temp must be defined by user)
cli ; Disable interrupts during timed sequence
sbi EECR, EEMWE ; Start EEPROM write
sbi EECR, EEWE
out SREG, temp ; Restore SREG value (I-flag)
Words: 1 (2 bytes)
Cycles: 1
1001 0100 1111 1000
I T H S V N Z C
0 – – – – – – –

53
AVR Instruction Set
0856C–09/01
CLN – Clear Negative Flag
Description:
Clears the Negative flag (N) in SREG (status register).
Operation:
(i) N ← 0
(i) CLN None PC ← PC + 1
16-bit Opcode:
N: 0
Negative flag cleared
Example:
cln ; Clear negative flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 1010 1000
I T H S V N Z C
– – – – – 0 – –

0856C–09/01
CLR – Clear Register
Description:
Clears a register. This instruction performs an Exclusive OR between a register and itself. This will clear all bits in the
register.
Operation:
(i) Rd ← Rd ⊕ Rd
(i) CLR Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode: (see EOR Rd,Rd)
S: 0
Cleared
V: 0
Cleared
N: 0
Cleared
Z: 1
Set
Example:
clr r18 ; clear r18
loop: inc r18 ; increase r18
...
cpi r18,$50 ; Compare r18 to $50
brne loop
Words: 1 (2 bytes)
Cycles: 1
0010 01dd dddd dddd
I T H S V N Z C
– – – 0 0 0 1 –

55
AVR Instruction Set
0856C–09/01
CLS – Clear Signed Flag
Description:
Clears the Signed flag (S) in SREG (status register).
Operation:
(i) S ← 0
(i) CLS None PC ← PC + 1
16-bit Opcode:
S: 0
Signed flag cleared
Example:
cls ; Clear signed flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 1100 1000
I T H S V N Z C
– – – 0 – – – –

0856C–09/01
CLT – Clear T Flag
Description:
Clears the T flag in SREG (status register).
Operation:
(i) T ← 0
(i) CLT None PC ← PC + 1
16-bit Opcode:
T: 0
T flag cleared
Example:
clt ; Clear T flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 1110 1000
I T H S V N Z C
– 0 – – – – – –

57
AVR Instruction Set
0856C–09/01
CLV – Clear Overflow Flag
Description:
Clears the Overflow flag (V) in SREG (status register).
Operation:
(i) V ← 0
(i) CLV None PC ← PC + 1
16-bit Opcode:
V: 0
Overflow flag cleared
Example:
clv ; Clear overflow flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 1011 1000
I T H S V N Z C
– – – – 0 – – –

0856C–09/01
CLZ – Clear Zero Flag
Description:
Clears the Zero flag (Z) in SREG (status register).
Operation:
(i) Z ← 0
(i) CLZ None PC ← PC + 1
16-bit Opcode:
Z: 0
Zero flag cleared
Example:
clz ; Clear zero
Words: 1 (2 bytes)
Cycles: 1
1001 0100 1001 1000
I T H S V N Z C
– – – – – – 0 –

59
AVR Instruction Set
0856C–09/01
COM – One’s Complement
Description:
This instruction performs a one’s complement of register Rd.
Operation:
(i) Rd ← $FF - Rd
(i) COM Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
S: N ⊕ V
For signed tests.
V: 0
Cleared.
N: R7
Z: R7 •R6• R5• R4 •R3 •R2• R1 •R0
Set if the result is $00; Cleared otherwise.
C: 1
Set.
Example:
com r4 ; Take one’s complement of r4
breq zero ; Branch if zero
...
zero: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1
1001 010d dddd 0000
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ 1

0856C–09/01
CP – Compare
Description:
This instruction performs a compare between two registers Rd and Rr. None of the registers are changed. All conditional
branches can be used after this instruction.
Operation:
(i) Rd - Rr
(i) CP Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
H: Rd3 •Rr3+ Rr3 •R3 +R3• Rd3
Set if there was a borrow from bit 3; cleared otherwise
V: Rd7• Rd7 •R7+ Rd7 •Rr7 •R7
N: R7
Z: R7• R6 •R5• R4 •R3 •R2 •R1 •R0
C: Rd7 •Rr7+ Rr7• R7 +R7• Rd7
Set if the absolute value of the contents of Rr is larger than the absolute value of Rd; cleared otherwise.
R (Result) after the operation.
Example:
cp r4,r19 ; Compare r4 with r19
brne noteq ; Branch if r4 <> r19
...
noteq: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1
0001 01rd dddd rrrr
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

61
AVR Instruction Set
0856C–09/01
CPC – Compare with Carry
Description:
This instruction performs a compare between two registers Rd and Rr and also takes into account the previous carry. None
of the registers are changed. All conditional branches can be used after this instruction.
Operation:
(i) Rd - Rr - C
(i) CPC Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
H: Rd3 •Rr3+ Rr3 •R3 +R3 •Rd3
V: Rd7 •Rr7• R7+ Rd7• Rr7 •R7
N: R7
Z: R7 •R6• R5• R4 •R3 •R2 •R1• R0 •Z
Previous value remains unchanged when the result is zero; cleared otherwise.
C: Rd7 •Rr7+ Rr7• R7 +R7 •Rd7
Set if the absolute value of the contents of Rr plus previous carry is larger than the absolute value of Rd; cleared
otherwise.
Example:
; Compare r3:r2 with r1:r0
cp r2,r0 ; Compare low byte
cpc r3,r1 ; Compare high byte
brne noteq ; Branch if not equal
...
0000 01rd dddd rrrr
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

0856C–09/01
Words: 1 (2 bytes)
Cycles: 1

63
AVR Instruction Set
0856C–09/01
CPI – Compare with Immediate
Description:
This instruction performs a compare between register Rd and a constant. The register is not changed. All conditional
branches can be used after this instruction.
Operation:
(i) Rd - K
(i) CPI Rd,K 16 ≤ d ≤ 31, 0≤ K ≤ 255 PC ← PC + 1
16-bit Opcode:
H: Rd3 •K3+ K3• R3+ R3 •Rd3
V: Rd7 •K7 •R7 +Rd7 •K7 •R7
N: R7
Z: R7 •R6• R5 •R4• R3• R2 •R1 •R0
C: Rd7 •K7 +K7 •R7+ R7 •Rd7
Set if the absolute value of K is larger than the absolute value of Rd; cleared otherwise.
Example:
cpi r19,3 ; Compare r19 with 3
brne error ; Branch if r19<>3
...
error: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1
0011 KKKK dddd KKKK
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

0856C–09/01
CPSE – Compare Skip if Equal
Description:
This instruction performs a compare between two registers Rd and Rr, and skips the next instruction if Rd = Rr.
Operation:
(i) If Rd = Rr then PC ← PC + 2 (or 3) else PC ← PC + 1
(i) CPSE Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1, Condition false - no skip
PC ← PC + 2, Skip a one word instruction
PC ← PC + 3, Skip a two word instruction
16-bit Opcode:
Example:
inc r4 ; Increase r4
cpse r4,r0 ; Compare r4 to r0
neg r4 ; Only executed if r4<>r0
Words: 1 (2 bytes)
Cycles: 1 if condition is false (no skip)
2 if condition is true (skip is executed) and the instruction skipped is 1 word
3 if condition is true (skip is executed) and the instruction skipped is 2 words
0001 00rd dddd rrrr
I T H S V N Z C
– – – – – – – –

65
AVR Instruction Set
0856C–09/01
DEC – Decrement
Description:
Subtracts one -1- from the contents of register Rd and places the result in the destination register Rd.
The C flag in SREG is not affected by the operation, thus allowing the DEC instruction to be used on a loop counter in mul-
tiple-precision computations.
When operating on unsigned values, only BREQ and BRNE branches can be expected to perform consistently. When
operating on two’s complement values, all signed branches are available.
Operation:
(i) Rd ← Rd - 1
(i) DEC Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
Status Register and Boolean Formula:
S: N ⊕ V
For signed tests.
V: R7 •R6 •R5 •R4• R3• R2 •R1• R0
Set if two’s complement overflow resulted from the operation; cleared otherwise. Two’s complement overflow occurs
if and only if Rd was $80 before the operation.
N: R7
Z: R7 •R6• R5 •R4• R3• R2• R1• R0
Example:
ldi r17,$10 ; Load constant in r17
loop: add r1,r2 ; Add r2 to r1
dec r17 ; Decrement r17
brne loop ; Branch if r17<>0
Words: 1 (2 bytes)
Cycles: 1
1001 010d dddd 1010
I T H S V N Z C
– – – ⇔ ⇔ ⇔ ⇔ –

0856C–09/01
EICALL – Extended Indirect Call to Subroutine
Description:
Indirect call of a subroutine pointed to by the Z (16 bits) pointer register in the register file and the EIND register in the I/O
space. This instruction allows for indirect calls to the entire program memory space. The stack pointer uses a post-decre-
ment scheme during EICALL.
This instruction is not implemented for devices with 2 bytes PC, see ICALL. Refer to the device specific instruction set
summary.
Operation:
(i) PC(15:0) ← Z(15:0)
PC(21:16) ←=EIND
Syntax: Operands: Program Counter: Stack:
(i) EICALL None See Operation STACK ← PC + 1
SP ← SP - 3 (3 bytes, 22 bits)
16-bit Opcode:
Example:
ldi r16,$05 ; Set up EIND and Z pointer
out EIND,r16
ldi r30,$00
ldi r31,$10
eicall ; Call to $051000
Words: 1 (2 bytes)
Cycles: 4 (only implemented in devices with 22 bit PC)
1001 0101 0001 1001
I T H S V N Z C
– – – – – – – –

67
AVR Instruction Set
0856C–09/01
EIJMP – Extended Indirect Jump
Description:
Indirect jump to the address pointed to by the Z (16 bits) pointer register in the register file and the EIND register in the I/O
space. This instruction allows for indirect jumps to the entire program memory space.
Operation:
(i) PC(15:0) ← Z(15:0)
PC(21:16) ←=EIND
(i) EIJMP None See Operation Not Affected
16-bit Opcode:
Example:
ldi r16,$05 ; Set up EIND and Z pointer
out EIND,r16
ldi r30,$00
ldi r31,$10
eijmp ; Jump to $051000
Words: 1 (2 bytes)
Cycles: 2
1001 0100 0001 1001
I T H S V N Z C
– – – – – – – –

0856C–09/01
ELPM – Extended Load Program Memory
Description:
Loads one byte pointed to by the Z register and the RAMPZ register in the I/O space, and places this byte in the destination
register Rd. This instruction features a 100% space effective constant initialization or constant data fetch. The program
memory is organized in 16-bit words while the Z pointer is a byte address. Thus, the least significant bit of the Z pointer
selects either low byte (ZLSB = 0) or high byte (ZLSB = 1). This instruction can address the entire program memory space.
The Z pointer register can either be left unchanged by the operation, or it can be incremented. The incrementation applies
to the entire 24-bit concatenation of the RAMPZ and Z pointer registers.
Devices with Self-Programming capability can use the ELPM instruction to read the fuse and lock bit value. Refer to the
device documentation for a detailed description.
The result of these combinations is undefined:
ELPM r30, Z+
ELPM r31, Z+
Operation: Comment:
(i) R0 ← (RAMPZ:Z) RAMPZ:Z: Unchanged, R0 implied destination register
(ii) Rd ← (RAMPZ:Z) RAMPZ:Z: Unchanged
(iii) Rd ← (RAMPZ:Z) (RAMPZ:Z) ← (RAMPZ:Z) + 1 RAMPZ:Z: Post incremented
(i) ELPM None, R0 implied PC ← PC + 1
(ii) ELPM Rd, Z 0 ≤ d ≤ 31 PC ← PC + 1
(iii) ELPM Rd, Z+ 0 ≤ d ≤ 31 PC ← PC + 1
16 bit Opcode:
Example:
ldi ZL, byte3(Table_1<<1); Initialize Z pointer
out RAMPZ, ZL
ldi ZH, byte2(Table_1<<1)
ldi ZL, byte1(Table_1<<1)
elpm r16, Z+ ; Load constant from program
; memory pointed to by RAMPZ:Z (Z is r31:r30)
...
Table_1:
.dw 0x3738 ; 0x38 is addressed when ZLSB = 0
; 0x37 is addressed when ZLSB = 1
(i) 1001 0101 1101 1000
(ii) 1001 000d dddd 0110
(iii) 1001 000d dddd 0111
I T H S V N Z C
– – – – – – – –

69
AVR Instruction Set
0856C–09/01
...
Words: 1 (2 bytes)
Cycles: 3

0856C–09/01
EOR – Exclusive OR
Description:
Performs the logical EOR between the contents of register Rd and register Rr and places the result in the destination regis-
ter Rd.
Operation:
(i) Rd ← Rd ⊕ Rr
(i) EOR Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
V: 0
Cleared
N: R7
Z: R7 •R6 •R5 •R4• R3• R2 •R1• R0
Example:
eor r0,r22 ; Bitwise exclusive or between r0 and r22
Words: 1 (2 bytes)
Cycles: 1
0010 01rd dddd rrrr
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ –

71
AVR Instruction Set
0856C–09/01
FMUL – Fractional Multiply Unsigned
Description:
This instruction performs 8-bit × 8-bit → 16-bit unsigned multiplication and shifts the result one bit left.
Let (N.Q) denote a fractional number with N binary digits left of the radix point, and Q binary digits right of the radix point. A
multiplication between two numbers in the formats (N1.Q1) and (N2.Q2) results in the format ((N1+N2).(Q1+Q2)). For sig-
nal processing applications, the format (1.7) is widely used for the inputs, resulting in a (2.14) format for the product. A left
shift is required for the high byte of the product to be in the same format as the inputs. The FMUL instruction incorporates
the shift operation in the same number of cycles as MUL.
The (1.7) format is most commonly used with signed numbers, while FMUL performs an unsigned multiplication. This
instruction is therefore most useful for calculating one of the partial products when performing a signed multiplication with
16-bit inputs in the (1.15) format, yielding a result in the (1.31) format. Note: the result of the FMUL operation may suffer
from a 2’s complement overflow if interpreted as a number in the (1.15) format. The MSB of the multiplication before shift-
ing must be taken into account, and is found in the carry bit. See the following example.
The multiplicand Rd and the multiplier Rr are two registers containing unsigned fractional numbers where the implicit radix
point lies between bit 6 and bit 7. The 16-bit unsigned fractional product with the implicit radix point between bit 14 and bit
15 is placed in R1 (high byte) and R0 (low byte).
Operation:
(i) R1:R0 ← Rd × Rr (unsigned (1.15) ← unsigned (1.7) ×=unsigned (1.7))
(i) FMUL Rd,Rr 16 ≤ d ≤ 23, 16≤ r ≤ 23 PC ← PC + 1
16-bit Opcode:
C: R16
Set if bit 15 of the result before left shift is set; cleared otherwise.
R (Result) equals R1,R0 after the operation.
Rd Rr R1 R0
Multiplicand × Multiplier Æ Product High Product Low
8 8 16
0000 0011 0ddd 1rrr
I T H S V N Z C
– – – – – – ⇔ ⇔

0856C–09/01
Example:
;******************************************************************************
;* DESCRIPTION
;*Signed fractional multiply of two 16-bit numbers with 32-bit result.
;* USAGE
;*r19:r18:r17:r16 = ( r23:r22 * r21:r20 ) << 1
;******************************************************************************
fmuls16x16_32:
clrr2
fmulsr23, r21;((signed)ah * (signed)bh) << 1
movwr19:r18, r1:r0
fmulr22, r20;(al * bl) << 1
adcr18, r2
movwr17:r16, r1:r0
fmulsur23, r20;((signed)ah * bl) << 1
sbcr19, r2
addr17, r0
adcr18, r1
adcr19, r2
fmulsur21, r22;((signed)bh * al) << 1
sbcr19, r2
addr17, r0
adcr18, r1
adcr19, r2
Words: 1 (2 bytes)
Cycles: 2

73
AVR Instruction Set
0856C–09/01
FMULS – Fractional Multiply Signed
Description:
This instruction performs 8-bit × 8-bit → 16-bit signed multiplication and shifts the result one bit left.
shift is required for the high byte of the product to be in the same format as the inputs. The FMULS instruction incorporates
the shift operation in the same number of cycles as MULS.
The multiplicand Rd and the multiplier Rr are two registers containing signed fractional numbers where the implicit radix
point lies between bit 6 and bit 7. The 16-bit signed fractional product with the implicit radix point between bit 14 and bit 15
is placed in R1 (high byte) and R0 (low byte).
Note that when multiplying 0x80 (-1) with 0x80 (-1), the result of the shift operation is 0x8000 (-1). The shift operation thus
gives a two’s complement overflow. This must be checked and handled by software.
Operation:
(i) R1:R0 ← Rd × Rr (signed (1.15) ← signed (1.7) ×=signed (1.7))
(i) FMULS Rd,Rr 16 ≤ d ≤ 23, 16≤ r ≤ 23 PC ← PC + 1
16-bit Opcode:
C: R16
Example:
fmuls r23,r22 ; Multiply signed r23 and r22 in (1.7) format, result in (1.15) format
movw r23:r22,r1:r0 ; Copy result back in r23:r22
Rd Rr R1 R0
Multiplicand × Multiplier → Product High Product Low
8 8 16
0000 0011 1ddd 0rrr
I T H S V N Z C
– – – – – – ⇔ ⇔

0856C–09/01
Words: 1 (2 bytes)
Cycles: 2

75
AVR Instruction Set
0856C–09/01
FMULSU – Fractional Multiply Signed with Unsigned
Description:
This instruction performs 8-bit × 8-bit → 16-bit signed multiplication and shifts the result one bit left.
shift is required for the high byte of the product to be in the same format as the inputs. The FMULSU instruction incorpo-
rates the shift operation in the same number of cycles as MULSU.
The (1.7) format is most commonly used with signed numbers, while FMULSU performs a multiplication with one unsigned
and one signed input. This instruction is therefore most useful for calculating two of the partial products when performing a
signed multiplication with 16-bit inputs in the (1.15) format, yielding a result in the (1.31) format. Note: the result of the
FMULSU operation may suffer from a 2's complement overflow if interpreted as a number in the (1.15) format. The MSB of
the multiplication before shifting must be taken into account, and is found in the carry bit. See the following example.
The multiplicand Rd and the multiplier Rr are two registers containing fractional numbers where the implicit radix point lies
between bit 6 and bit 7. The multiplicand Rd is a signed fractional number, and the multiplier Rr is an unsigned fractional
number. The 16-bit signed fractional product with the implicit radix point between bit 14 and bit 15 is placed in R1 (high
byte) and R0 (low byte).
Operation:
(i) R1:R0 ← Rd × Rr (signed (1.15) ← signed (1.7) ×=unsigned (1.7))
(i) FMULSU Rd,Rr 16 ≤ d ≤ 23, 16≤ r ≤ 23 PC ← PC + 1
16-bit Opcode:
C: R16
Rd Rr R1 R0
8 8 16
0000 0011 1ddd 1rrr
I T H S V N Z C
– – – – – – ⇔ ⇔

0856C–09/01
Example:
;******************************************************************************
;* DESCRIPTION
;*Signed fractional multiply of two 16-bit numbers with 32-bit result.
;* USAGE
;*r19:r18:r17:r16 = ( r23:r22 * r21:r20 ) << 1
;******************************************************************************
fmuls16x16_32:
clrr2
fmulsr23, r21;((signed)ah * (signed)bh) << 1
movwr19:r18, r1:r0
fmulr22, r20;(al * bl) << 1
adcr18, r2
movwr17:r16, r1:r0
fmulsur23, r20;((signed)ah * bl) << 1
sbcr19, r2
addr17, r0
adcr18, r1
adcr19, r2
fmulsur21, r22;((signed)bh * al) << 1
sbcr19, r2
addr17, r0
adcr18, r1
adcr19, r2
Words: 1 (2 bytes)
Cycles: 2

77
AVR Instruction Set
0856C–09/01
ICALL – Indirect Call to Subroutine
Description:
Indirect call of a subroutine pointed to by the Z (16 bits) pointer register in the register file. The Z pointer register is 16 bits
wide and allows call to a subroutine within the lowest 64K words (128K bytes) section in the program memory space. The
stack pointer uses a post-decrement scheme during ICALL.
Operation:
(i) PC(15:0) ← Z(15:0) Devices with 16 bits PC, 128K bytes program memory maximum.
(ii) PC(15:0) ← Z(15:0) Devices with 22 bits PC, 8M bytes program memory maximum.
PC(21:16) ← 0
(i) ICALL None See Operation STACK ← PC + 1
(ii) ICALL None See Operation STACK ← PC + 1
16-bit Opcode:
Example:
mov r30,r0 ; Set offset to call table
icall ; Call routine pointed to by r31:r30
Words: 1 (2 bytes)
Cycles: 3 devices with 16 bit PC
4 devices with 22 bit PC
1001 0101 0000 1001
I T H S V N Z C
– – – – – – – –

0856C–09/01
IJMP – Indirect Jump
Description:
Indirect jump to the address pointed to by the Z (16 bits) pointer register in the register file. The Z pointer register is 16 bits
wide and allows jump within the lowest 64K words (128K bytes) section of program memory.
Operation:
(i) PC ← Z(15:0) Devices with 16 bits PC, 128K bytes program memory maximum.
(ii) PC(15:0) ← Z(15:0) Devices with 22 bits PC, 8M bytes program memory maximum.
PC(21:16) ← 0
(i),(ii) IJMP None See Operation Not Affected
16-bit Opcode:
Example:
mov r30,r0 ; Set offset to jump table
ijmp ; Jump to routine pointed to by r31:r30
Words: 1 (2 bytes)
Cycles: 2
1001 0100 0000 1001
I T H S V N Z C
– – – – – – – –

79
AVR Instruction Set
0856C–09/01
IN - Load an I/O Location to Register
Description:
Loads data from the I/O Space (Ports, Timers, Configuration registers etc.) into register Rd in the register file.
Operation:
(i) Rd ← I/O(A)
(i) IN Rd,A 0 ≤ d ≤ 31, 0 ≤=A ≤ 63 PC ← PC + 1
16-bit Opcode:
Example:
in r25,$16 ; Read Port B
cpi r25,4 ; Compare read value to constant
breq exit ; Branch if r25=4
...
exit: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1
1011 0AAd dddd AAAA
I T H S V N Z C
– – – – – – – –

0856C–09/01
INC – Increment
Description:
Adds one -1- to the contents of register Rd and places the result in the destination register Rd.
The C flag in SREG is not affected by the operation, thus allowing the INC instruction to be used on a loop counter in mul-
tiple-precision computations.
When operating on unsigned numbers, only BREQ and BRNE branches can be expected to perform consistently. When
operating on two’s complement values, all signed branches are available.
Operation:
(i) Rd ← Rd + 1
(i) INC Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
S: N ⊕ V
For signed tests.
V: R7 •R6 •R5 •R4 •R3• R2 •R1 •R0
Set if two’s complement overflow resulted from the operation; cleared otherwise. Two’s complement overflow occurs
if and only if Rd was $7F before the operation.
N: R7
Z: R7 •R6 •R5 •R4•R3 •R2• R1• R0
Example:
clr r22 ; clear r22
loop: inc r22 ; increment r22
...
cpi r22,$4F ; Compare r22 to $4f
brne loop ; Branch if not equal
1001 010d dddd 0011
I T H S V N Z C
– – – ⇔ ⇔ ⇔ ⇔ –

81
AVR Instruction Set
0856C–09/01
Words: 1 (2 bytes)
Cycles: 1

0856C–09/01
JMP – Jump
Description:
Jump to an address within the entire 4M (words) program memory. See also RJMP.
Operation:
(i) PC ← k
(i) JMP k 0 ≤ k < 4M PC ← k Unchanged
32-bit Opcode:
Example:
jmp farplc ; Unconditional jump
...
farplc: nop ; Jump destination (do nothing)
Words: 2 (4 bytes)
Cycles: 3
1001 010k kkkk 110k
kkkk kkkk kkkk kkkk
I T H S V N Z C
– – – – – – – –

83
AVR Instruction Set
0856C–09/01
LD – Load Indirect from Data Space to Register using Index X
Description:
Loads one byte indirect from the data space to a register. For parts with SRAM, the data space consists of the register file,
I/O memory and internal SRAM (and external SRAM if applicable). For parts without SRAM, the data space consists of the
register file only. The EEPROM has a separate address space.
The data location is pointed to by the X (16 bits) pointer register in the register file. Memory access is limited to the current
data segment of 64K bytes. To access another data segment in devices with more than 64K bytes data space, the RAMPX
in register in the I/O area has to be changed.
The X pointer register can either be left unchanged by the operation, or it can be post-incremented or pre-decremented.
These features are especially suited for accessing arrays, tables, and stack pointer usage of the X pointer register. Note
that only the low byte of the X pointer is updated in devices with no more than 256 bytes data space. For such devices, the
high byte of the pointer is not used by this instruction and can be used for other purposes. The RAMPX register in the I/O
area is updated in parts with more than 64K bytes data space or more than 64K bytes program memory, and the incre-
ment/decrement is added to the entire 24-bit address on such devices.
Not all variants of this instruction is available in all devices. Refer to the device specific instruction set summary.
LD r26, X+
LD r27, X+
LD r26, -X
LD r27, -X
Using the X pointer:
Operation: Comment:
(i) Rd ← (X) X: Unchanged
(ii) Rd ← (X) X ← X + 1 X: Post incremented
(iii) X ← X - 1 Rd ← (X) X: Pre decremented
(i) LD Rd, X 0 ≤ d ≤ 31 PC ← PC + 1
(ii) LD Rd, X+ 0 ≤ d ≤ 31 PC ← PC + 1
(iii) LD Rd, -X 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
Example:
clr r27 ; Clear X high byte
ldi r26,$60 ; Set X low byte to $60
(i) 1001 000d dddd 1100
(ii) 1001 000d dddd 1101
(iii) 1001 000d dddd 1110
I T H S V N Z C
– – – – – – – –

0856C–09/01
ld r0,X+ ; Load r0 with data space loc. $60(X post inc)
ld r1,X ; Load r1 with data space loc. $61
ld r2,X ; Load r2 with data space loc. $63
ld r3,–X ; Load r3 with data space loc. $62(X pre dec)
Words: 1 (2 bytes)
Cycles: 2

85
AVR Instruction Set
0856C–09/01
LD (LDD) – Load Indirect from Data Space to Register using Index Y
Description:
Loads one byte indirect with or without displacement from the data space to a register. For parts with SRAM, the data
space consists of the register file, I/O memory and internal SRAM (and external SRAM if applicable). For parts without
SRAM, the data space consists of the register file only. The EEPROM has a separate address space.
The data location is pointed to by the Y (16 bits) pointer register in the register file. Memory access is limited to the current
data segment of 64K bytes. To access another data segment in devices with more than 64K bytes data space, the RAMPY
The Y pointer register can either be left unchanged by the operation, or it can be post-incremented or pre-decremented.
These features are especially suited for accessing arrays, tables, and stack pointer usage of the Y pointer register. Note
that only the low byte of the Y pointer is updated in devices with no more than 256 bytes data space. For such devices, the
high byte of the pointer is not used by this instruction and can be used for other purposes. The RAMPY register in the I/O
area is updated in parts with more than 64K bytes data space or more than 64K bytes program memory, and the incre-
ment/decrement/displacement is added to the entire 24-bit address on such devices.
LD r28, Y+
LD r29, Y+
LD r28, -Y
LD r29, -Y
Using the Y pointer:
Operation: Comment:
(i) Rd ← (Y) Y: Unchanged
(ii) Rd ← (Y) Y ← Y + 1 Y: Post incremented
(iii) Y ← Y - 1 Rd ← (Y) Y: Pre decremented
(iiii) Rd ← (Y+q) Y: Unchanged, q: Displacement
(i) LD Rd, Y 0 ≤ d ≤ 31 PC ← PC + 1
(ii) LD Rd, Y+ 0 ≤ d ≤ 31 PC ← PC + 1
(iii) LD Rd, -Y 0 ≤ d ≤ 31 PC ← PC + 1
(iiii) LDD Rd, Y+q 0 ≤ d ≤ 31, 0 ≤ q ≤ 63 PC ← PC + 1

0856C–09/01
16-bit Opcode:
Example:
clr r29 ; Clear Y high byte
ldi r28,$60 ; Set Y low byte to $60
ld r0,Y+ ; Load r0 with data space loc. $60(Y post inc)
ld r1,Y ; Load r1 with data space loc. $61
ld r2,Y ; Load r2 with data space loc. $63
ld r3,-Y ; Load r3 with data space loc. $62(Y pre dec)
ldd r4,Y+2 ; Load r4 with data space loc. $64
Words: 1 (2 bytes)
Cycles: 2
(i) 1000 000d dddd 1000
(ii) 1001 000d dddd 1001
(iii) 1001 000d dddd 1010
(iiii) 10q0 qq0d dddd 1qqq
I T H S V N Z C
– – – – – – – –

87
AVR Instruction Set
0856C–09/01
LD (LDD) – Load Indirect From Data Space to Register using Index Z
Description:
Loads one byte indirect with or without displacement from the data space to a register. For parts with SRAM, the data
space consists of the register file, I/O memory and internal SRAM (and external SRAM if applicable). For parts without
SRAM, the data space consists of the register file only. The EEPROM has a separate address space.
The data location is pointed to by the Z (16 bits) pointer register in the register file. Memory access is limited to the current
data segment of 64K bytes. To access another data segment in devices with more than 64K bytes data space, the RAMPZ
The Z pointer register can either be left unchanged by the operation, or it can be post-incremented or pre-decremented.
These features are especially suited for stack pointer usage of the Z pointer register, however because the Z pointer regis-
ter can be used for indirect subroutine calls, indirect jumps and table lookup, it is often more convenient to use the X or Y
pointer as a dedicated stack pointer. Note that only the low byte of the Z pointer is updated in devices with no more than
256 bytes data space. For such devices, the high byte of the pointer is not used by this instruction and can be used for
other purposes. The RAMPZ register in the I/O area is updated in parts with more than 64K bytes data space or more than
64K bytes program memory, and the increment/decrement/displacement is added to the entire 24-bit address on such
devices.
For using the Z pointer for table lookup in program memory see the LPM and ELPM instructions.
LD r30, Z+
LD r31, Z+
LD r30, -Z
LD r31, -Z
Using the Z pointer:
Operation: Comment:
(i) Rd ← (Z) Z: Unchanged
(ii) Rd ← (Z) Z ← Z + 1 Z: Post increment
(iii) Z ← Z -1 Rd ← (Z) Z: Pre decrement
(iiii) Rd ← (Z+q) Z: Unchanged, q: Displacement
(i) LD Rd, Z 0 ≤ d ≤ 31 PC ← PC + 1
(ii) LD Rd, Z+ 0 ≤ d ≤ 31 PC ← PC + 1
(iii) LD Rd, -Z 0 ≤ d ≤ 31 PC ← PC + 1
(iiii) LDD Rd, Z+q 0 ≤ d ≤ 31, 0 ≤ q ≤ 63 PC ← PC + 1

0856C–09/01
16-bit Opcode:
Example:
clr r31 ; Clear Z high byte
ldi r30,$60 ; Set Z low byte to $60
ld r0,Z+ ; Load r0 with data space loc. $60(Z post inc)
ld r1,Z ; Load r1 with data space loc. $61
ld r2,Z ; Load r2 with data space loc. $63
ld r3,-Z ; Load r3 with data space loc. $62(Z pre dec)
ldd r4,Z+2 ; Load r4 with data space loc. $64
Words: 1 (2 bytes)
Cycles: 2
(i) 1000 000d dddd 0000
(ii) 1001 000d dddd 0001
(iii) 1001 000d dddd 0010
(iiii) 10q0 qq0d dddd 0qqq
I T H S V N Z C
– – – – – – – –

89
AVR Instruction Set
0856C–09/01
LDI – Load Immediate
Description:
Loads an 8 bit constant directly to register 16 to 31.
Operation:
(i) Rd ← K
(i) LDI Rd,K 16 ≤ d ≤ 31, 0 ≤ K ≤ 255 PC ← PC + 1
16-bit Opcode:
Example:
ldi r30,$F0 ; Set Z low byte to $F0
lpm ; Load constant from program
; memory pointed to by Z
Words: 1 (2 bytes)
Cycles: 1
1110 KKKK dddd KKKK
I T H S V N Z C
– – – – – – – –

0856C–09/01
LDS – Load Direct from Data Space
Description:
Loads one byte from the data space to a register. For parts with SRAM, the data space consists of the register file, I/O
memory and internal SRAM (and external SRAM if applicable). For parts without SRAM, the data space consists of the reg-
ister file only. The EEPROM has a separate address space.
A 16-bit address must be supplied. Memory access is limited to the current data segment of 64K bytes. The LDS instruction
uses the RAMPD register to access memory above 64K bytes. To access another data segment in devices with more than
64K bytes data space, the RAMPD in register in the I/O area has to be changed.
Operation:
(i) Rd ← (k)
(i) LDS Rd,k 0 ≤ d ≤ 31, 0 ≤ k ≤ 65535 PC ← PC + 2
32-bit Opcode:
Example:
lds r2,$FF00 ; Load r2 with the contents of data space location $FF00
add r2,r1 ; add r1 to r2
sts $FF00,r2 ; Write back
Words: 2 (4 bytes)
Cycles: 2
1001 000d dddd 0000
kkkk kkkk kkkk kkkk
I T H S V N Z C
– – – – – – – –

91
AVR Instruction Set
0856C–09/01
LPM – Load Program Memory
Description:
Loads one byte pointed to by the Z register into the destination register Rd. This instruction features a 100% space effec-
tive constant initialization or constant data fetch. The program memory is organized in 16-bit words while the Z pointer is a
byte address. Thus, the least significant bit of the Z pointer selects either low byte (ZLSB = 0) or high byte (ZLSB = 1). This
instruction can address the first 64K bytes (32K words) of program memory. The Z pointer register can either be left
unchanged by the operation, or it can be incremented. The incrementation does not apply to the RAMPZ register.
Devices with Self-Programming capability can use the LPM instruction to read the fuse and lock bit values. Refer to the
device documentation for a detailed description.
Not all variants of the LPM instruction are available in all devices. Refer to the device specific instruction set summary. The
LPM instruction is not implemented at all in the AT90S1200 device.
LPM r30, Z+
LPM r31, Z+
Operation: Comment:
(i) R0 ← (Z) Z: Unchanged, R0 implied destination register
(ii) Rd ← (Z) Z: Unchanged
(iii) Rd ← (Z) Z ← Z + 1 Z: Post incremented
(i) LPM None, R0 implied PC ← PC + 1
(ii) LPM Rd, Z 0 ≤ d ≤ 31 PC ← PC + 1
(iii) LPM Rd, Z+ 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
Example:
ldi ZH, high(Table_1<<1); Initialize Z pointer
ldi ZL, low(Table_1<<1)
lpm r16, Z ; Load constant from program
; memory pointed to by Z (r31:r30)
...
Table_1:
.dw 0x5876 ; 0x76 is addresses when ZLSB = 0
; 0x58 is addresses when ZLSB = 1
...
(i) 1001 0101 1100 1000
(ii) 1001 000d dddd 0100
(iii) 1001 000d dddd 0101
I T H S V N Z C
– – – – – – – –

0856C–09/01
Words: 1 (2 bytes)
Cycles: 3

93
AVR Instruction Set
0856C–09/01
LSL – Logical Shift Left
Description:
Shifts all bits in Rd one place to the left. Bit 0 is cleared. Bit 7 is loaded into the C flag of the SREG. This operation effec-
tively multiplies signed and unsigned values by two.
Operation:
(i)
(i) LSL Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode: (see ADD Rd,Rd)
H: Rd3
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
C: Rd7
Set if, before the shift, the MSB of Rd was set; cleared otherwise.
Example:
lsl r0 ; Multiply r0 by 2
Words: 1 (2 bytes)
Cycles: 1
←
C ← b7 - - - - - - - - - - - - - - - - - - b0 ← 0
0000 11dd dddd dddd
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

0856C–09/01
LSR – Logical Shift Right
Description:
Shifts all bits in Rd one place to the right. Bit 7 is cleared. Bit 0 is loaded into the C flag of the SREG. This operation effec-
tively divides an unsigned value by two. The C flag can be used to round the result.
Operation:
(i) LSR Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
N: 0
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
C: Rd0
Example:
lsr r0 ; Divide r0 by 2
Words: 1 (2 bytes)
Cycles: 1
→
0 → b7 - - - - - - - - - - - - - - - - - - b0 → C
1001 010d dddd 0110
I T H S V N Z C
– – – ⇔ ⇔ 0 ⇔ ⇔

95
AVR Instruction Set
0856C–09/01
MOV – Copy Register
Description:
This instruction makes a copy of one register into another. The source register Rr is left unchanged, while the destination
register Rd is loaded with a copy of Rr.
Operation:
(i) Rd ← Rr
(i) MOV Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
Example:
...
check: cpi r16,$11 ; Compare r16 to $11
...
Words: 1 (2 bytes)
Cycles: 1
0010 11rd dddd rrrr
I T H S V N Z C
– – – – – – – –

0856C–09/01
MOVW – Copy Register Word
Description:
This instruction makes a copy of one register pair into another register pair. The source register pair Rr+1:Rr is left
unchanged, while the destination register pair Rd+1:Rd is loaded with a copy of Rr + 1:Rr.
Operation:
(i) Rd+1:Rd ← Rr+1:Rr
(i) MOVW Rd+1:Rd,Rr+1Rrd ∈ {0,2,...,30}, r ∈ {0,2,...,30} PC ← PC + 1
16-bit Opcode:
Example:
movw r17:16,r1:r0 ; Copy r1:r0 to r17:r16
...
check: cpi r16,$11 ; Compare r16 to $11
...
...
Words: 1 (2 bytes)
Cycles: 1
0000 0001 dddd rrrr
I T H S V N Z C
– – – – – – – –

97
AVR Instruction Set
0856C–09/01
MUL – Multiply Unsigned
Description:
This instruction performs 8-bit × 8-bit → 16-bit unsigned multiplication.
The multiplicand Rd and the multiplier Rr are two registers containing unsigned numbers. The 16-bit unsigned product is
placed in R1 (high byte) and R0 (low byte). Note that if the multiplicand or the multiplier is selected from R0 or R1 the result
will overwrite those after multiplication.
Operation:
(i) R1:R0 ← Rd × Rr (unsigned ← unsigned=×=unsigned)
(i) MUL Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
C: R15
Set if bit 15 of the result is set; cleared otherwise.
Example:
mul r5,r4 ; Multiply unsigned r5 and r4
movw r4,r0 ; Copy result back in r5:r4
Words: 1 (2 bytes)
Cycles: 2
Rd Rr R1 R0
8 8 16
1001 11rd dddd rrrr
I T H S V N Z C
– – – – – – ⇔ ⇔

0856C–09/01
MULS – Multiply Signed
Description:
This instruction performs 8-bit × 8-bit → 16-bit signed multiplication.
The multiplicand Rd and the multiplier Rr are two registers containing signed numbers. The 16-bit signed product is placed
in R1 (high byte) and R0 (low byte).
Operation:
(i) R1:R0 ← Rd × Rr (signed ← signed=×=signed)
(i) MULS Rd,Rr 16 ≤ d ≤ 31, 16 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
C: R15
Example:
muls r21,r20 ; Multiply signed r21 and r20
movw r20,r0 ; Copy result back in r21:r20
Words: 1 (2 bytes)
Cycles: 2
Rd Rr R1 R0
8 8 16
0000 0010 dddd rrrr
I T H S V N Z C
– – – – – – ⇔ ⇔

99
AVR Instruction Set
0856C–09/01
MULSU – Multiply Signed with Unsigned
Description:
This instruction performs 8-bit × 8-bit → 16-bit multiplication of a signed and an unsigned number.
The multiplicand Rd and the multiplier Rr are two registers. The multiplicand Rd is a signed number, and the multiplier Rr is
unsigned. The 16-bit signed product is placed in R1 (high byte) and R0 (low byte).
Operation:
(i) R1:R0 ← Rd × Rr (signed ← signed=×=unsigned)
(i) MULSU Rd,Rr 16 ≤ d ≤ 23, 16 ≤ r ≤ 23 PC ← PC + 1
16-bit Opcode:
C: R15
Example:
;******************************************************************************
;* DESCRIPTION
;*Signed multiply of two 16-bit numbers with 32-bit result.
;* USAGE
;*r19:r18:r17:r16 = r23:r22 * r21:r20
;******************************************************************************
muls16x16_32:
clrr2
mulsr23, r21; (signed)ah * (signed)bh
Rd Rr R1 R0
8 8 16
0000 0011 0ddd 0rrr
I T H S V N Z C
– – – – – – ⇔ ⇔

0856C–09/01
movwr19:r18, r1:r0
mulr22, r20; al * bl
movwr17:r16, r1:r0
mulsur23, r20; (signed)ah * bl
sbcr19, r2
addr17, r0
adcr18, r1
adcr19, r2
mulsur21, r22; (signed)bh * al
sbcr19, r2
addr17, r0
adcr18, r1
adcr19, r2
ret
Words: 1 (2 bytes)
Cycles: 2

101
AVR Instruction Set
0856C–09/01
NEG – Two’s Complement
Description:
Replaces the contents of register Rd with its two’s complement; the value $80 is left unchanged.
Operation:
(i) Rd ← $00 - Rd
(i) NEG Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
H: R3 + Rd3
S: N ⊕ V
For signed tests.
V: R7• R6 •R5• R4• R3 •R2• R1• R0
Set if there is a two’s complement overflow from the implied subtraction from zero; cleared otherwise. A two’s com-
plement overflow will occur if and only if the contents of the Register after operation (Result) is $80.
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
C: R7 + R6 + R5 + R4 + R3 + R2 + R1 + R0
Set if there is a borrow in the implied subtraction from zero; cleared otherwise. The C flag will be set in all cases
except when the contents of Register after operation is $00.
Example:
sub r11,r0 ; Subtract r0 from r11
brpl positive ; Branch if result positive
neg r11 ; Take two’s complement of r11
positive: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1
1001 010d dddd 0001
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

0856C–09/01
NOP – No Operation
Description:
This instruction performs a single cycle No Operation.
Operation:
(i) No
(i) NOP None PC ← PC + 1
16-bit Opcode:
Example:
clr r16 ; Clear r16
ser r17 ; Set r17
out $18,r16 ; Write zeros to Port B
nop ; Wait (do nothing)
out $18,r17 ; Write ones to Port B
Words: 1 (2 bytes)
Cycles: 1
0000 0000 0000 0000
I T H S V N Z C
– – – – – – – –

103
AVR Instruction Set
0856C–09/01
OR – Logical OR
Description:
Performs the logical OR between the contents of register Rd and register Rr and places the result in the destination register
Rd.
Operation:
(i) Rd ← Rd v Rr
(i) OR Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
V: 0
Cleared
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
Example:
or r15,r16 ; Do bitwise or between registers
brts ok ; Branch if T flag set
...
ok: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1
0010 10rd dddd rrrr
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ –

0856C–09/01
ORI – Logical OR with Immediate
Description:
Performs the logical OR between the contents of register Rd and a constant and places the result in the destination register
Rd.
Operation:
(i) Rd ← Rd v K
(i) ORI Rd,K 16 ≤ d ≤ 31, 0 ≤ K ≤ 255 PC ← PC + 1
16-bit Opcode:
V: 0
Cleared
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
Example:
ori r16,$F0 ; Set high nibble of r16
ori r17,1 ; Set bit 0 of r17
Words: 1 (2 bytes)
Cycles: 1
0110 KKKK dddd KKKK
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ –

105
AVR Instruction Set
0856C–09/01
OUT – Store Register to I/O Location
Description:
Stores data from register Rr in the register file to I/O Space (Ports, Timers, Configuration registers etc.).
Operation:
(i) I/O(A) ← Rr
(i) OUT A,Rr 0 ≤ r ≤ 31, 0 ≤ A ≤ 63 PC ← PC + 1
16-bit Opcode:
Example:
clr r16 ; Clear r16
ser r17 ; Set r17
nop ; Wait (do nothing)
Words: 1 (2 bytes)
Cycles: 1
1011 1AAr rrrr AAAA
I T H S V N Z C
– – – – – – – –

0856C–09/01
POP – Pop Register from Stack
Description:
This instruction loads register Rd with a byte from the STACK. The stack pointer is pre-incremented by 1 before the POP.
Operation:
(i) Rd ← STACK
(i) POP Rd 0 ≤ d ≤ 31 PC ← PC + 1 SP ← SP + 1
16-bit Opcode:
Example:
call routine ; Call subroutine
...
routine: push r14 ; Save r14 on the stack
push r13 ; Save r13 on the stack
...
pop r13 ; Restore r13
Words: 1 (2 bytes)
Cycles: 2
1001 000d dddd 1111
I T H S V N Z C
– – – – – – – –

107
AVR Instruction Set
0856C–09/01
PUSH – Push Register on Stack
Description:
This instruction stores the contents of register Rr on the STACK. The stack pointer is post-decremented by 1 after the
PUSH.
Operation:
(i) STACK ← Rr
(i) PUSH Rr 0 ≤ r ≤ 31 PC ← PC + 1 SP ← SP - 1
16-bit Opcode:
Example:
...
push r13 ; Save r13 on the stack
...
Words: 1 (2 bytes)
Cycles: 2
1001 001d dddd 1111
I T H S V N Z C
– – – – – – – –

0856C–09/01
RCALL – Relative Call to Subroutine
Description:
Relative call to an address within PC - 2K + 1 and PC + 2K (words). The return address (the instruction after the RCALL) is
stored onto the stack. (See also CALL). In the assembler, labels are used instead of relative operands. For AVR microcon-
trollers with program memory not exceeding 4K words (8K bytes) this instruction can address the entire memory from every
address location. The stack pointer uses a post-decrement scheme during RCALL.
Operation:
(i) PC ← PC + k + 1 Devices with 16 bits PC, 128K bytes program memory maximum.
(ii) PC ← PC + k + 1 Devices with 22 bits PC, 8M bytes program memory maximum.
(i) RCALL k -2K ≤ k < 2K PC ← PC + k + 1 STACK ← PC + 1
(ii) RCALL k -2K ≤ k < 2K PC ← PC + k + 1 STACK ← PC + 1
16-bit Opcode:
Example:
rcall routine ; Call subroutine
...
...
Words: 1 (2 bytes)
Cycles: 3 devices with 16-bit PC
4 devices with 22-bit PC
1101 kkkk kkkk kkkk
I T H S V N Z C
– – – – – – – –

109
AVR Instruction Set
0856C–09/01
RET – Return from Subroutine
Description:
Returns from subroutine. The return address is loaded from the STACK. The stack pointer uses a pre-increment scheme
during RET.
Operation:
(i) PC(15:0) ← STACKDevices with 16 bits PC, 128K bytes program memory maximum.
(ii) PC(21:0) ← STACKDevices with 22 bits PC, 8M bytes program memory maximum.
(i) RET None See Operation SP←SP + 2, (2bytes,16 bits)
(ii) RET None See Operation SP←SP + 3, (3bytes,22 bits)
16-bit Opcode:
Example:
...
...
Words: 1 (2 bytes)
1001 0101 0000 1000
I T H S V N Z C
– – – – – – – –

0856C–09/01
RETI – Return from Interrupt
Description:
Returns from interrupt. The return address is loaded from the STACK and the global interrupt flag is set.
Note that the status register is not automatically stored when entering an interrupt routine, and it is not restored when
returning from an interrupt routine. This must be handled by the application program. The stack pointer uses a pre-incre-
ment scheme during RETI.
Operation:
(i) PC(15:0) ← STACKDevices with 16 bits PC, 128K bytes program memory maximum.
(ii) PC(21:0) ← STACKDevices with 22 bits PC, 8M bytes program memory maximum.
Syntax: Operands: Program Counter: Stack
(i) RETI None See Operation SP ← SP + 2 (2 bytes, 16 bits)
(ii) RETI None See Operation SP ← SP + 3 (3 bytes, 22 bits)
16-bit Opcode:
I: 1
The I flag is set.
Example:
...
extint: push r0 ; Save r0 on the stack
...
pop r0 ; Restore r0
reti ; Return and enable interrupts
Words: 1 (2 bytes)
1001 0101 0001 1000
I T H S V N Z C
1 – – – – – – –

111
AVR Instruction Set
0856C–09/01
RJMP – Relative Jump
Description:
Relative jump to an address within PC - 2K +1 and PC + 2K (words). In the assembler, labels are used instead of relative
operands. For AVR microcontrollers with program memory not exceeding 4K words (8K bytes) this instruction can address
the entire memory from every address location.
Operation:
(i) PC ← PC + k + 1
Syntax: Operands: Program Counter: Stack
(i) RJMP k -2K ≤ k < 2K PC ← PC + k + 1 Unchanged
16-bit Opcode:
Example:
brne error ; Branch if r16 <> $42
rjmp ok ; Unconditional branch
error: add r16,r17 ; Add r17 to r16
inc r16 ; Increment r16
ok: nop ; Destination for rjmp (do nothing)
Words: 1 (2 bytes)
Cycles: 2
1100 kkkk kkkk kkkk
I T H S V N Z C
– – – – – – – –

0856C–09/01
ROL – Rotate Left trough Carry
Description:
Shifts all bits in Rd one place to the left. The C flag is shifted into bit 0 of Rd. Bit 7 is shifted into the C flag. This operation,
combined with LSL, effectively multiplies multi-byte signed and unsigned values by two.
Operation:
(i) ROL Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode: (see ADC Rd,Rd)
H: Rd3
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
C: Rd7
Set if, before the shift, the MSB of Rd was set; cleared otherwise.
Example:
lsl r18 ; Multiply r19:r18 by two
rol r19 ; r19:r18 is a signed or unsigned two-byte integer
brcs oneenc ; Branch if carry set
...
oneenc: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1
←
C ¨ b7 - - - - - - - - - - - - - - - - - - b0 ← C
0001 11dd dddd dddd
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

113
AVR Instruction Set
0856C–09/01
ROR – Rotate Right through Carry
Description:
Shifts all bits in Rd one place to the right. The C flag is shifted into bit 7 of Rd. Bit 0 is shifted into the C flag. This operation,
combined with ASR, effectively divides multi-byte signed values by two. Combined with LSR it effectively divides multi-byte
unsigned values by two. The carry flag can be used to round the result.
Operation:
(i) ROR Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
C: Rd0
Example:
lsr r19 ; Divide r19:r18 by two
ror r18 ; r19:r18 is an unsigned two-byte integer
brcc zeroenc1 ; Branch if carry cleared
asr r17 ; Divide r17:r16 by two
ror r16 ; r17:r16 is a signed two-byte integer
brcc zeroenc2 ; Branch if carry cleared
...
zeroenc1: nop ; Branch destination (do nothing)
...
→
C → b7 - - - - - - - - - - - - - - - - - - b0 → C
1001 010d dddd 0111
I T H S V N Z C
– – – ⇔ ⇔ ⇔ ⇔ ⇔

0856C–09/01
zeroenc1: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1

115
AVR Instruction Set
0856C–09/01
SBC – Subtract with Carry
Description:
Subtracts two registers and subtracts with the C flag and places the result in the destination register Rd.
Operation:
(i) Rd ← Rd - Rr - C
(i) SBC Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
H: Rd3• Rr3 + Rr3• R3 + R3 •Rd3
V: Rd7 •Rr7• R7 +Rd7 •Rr7 •R7
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0• Z
C: Rd7 •Rr7+ Rr7 •R7 +R7 •Rd7
Set if the absolute value of the contents of Rr plus previous carry is larger than the absolute value of the Rd; cleared
otherwise.
Example:
; Subtract r1:r0 from r3:r2
sub r2,r0 ; Subtract low byte
sbc r3,r1 ; Subtract with carry high byte
Words: 1 (2 bytes)
Cycles: 1
0000 10rd dddd rrrr
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

0856C–09/01
SBCI – Subtract Immediate with Carry
Description:
Subtracts a constant from a register and subtracts with the C flag and places the result in the destination register Rd.
Operation:
(i) Rd ← Rd - K - C
(i) SBCI Rd,K 16 ≤ d ≤ 31, 0 ≤ K ≤ 255 PC ← PC + 1
16-bit Opcode:
H: Rd3• K3 + K3• R3 + R3 •Rd3
V: Rd7 •K7• R7 +Rd7 •K7 •R7
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0• Z
C: Rd7 •K7+ K7 •=R7 +R7 •Rd7
Set if the absolute value of the constant plus previous carry is larger than the absolute value of Rd; cleared other-
wise.
Example:
; Subtract $4F23 from r17:r16
subi r16,$23 ; Subtract low byte
sbci r17,$4F ; Subtract with carry high byte
Words: 1 (2 bytes)
Cycles: 1
0100 KKKK dddd KKKK
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

117
AVR Instruction Set
0856C–09/01
SBI – Set Bit in I/O Register
Description:
Sets a specified bit in an I/O register. This instruction operates on the lower 32 I/O registers – addresses 0-31.
Operation:
(i) I/O(A,b) ← 1
(i) SBI A,b 0 ≤ A ≤ 31, 0 ≤ b ≤ 7 PC ← PC + 1
16-bit Opcode:
Example:
out $1E,r0 ; Write EEPROM address
sbi $1C,0 ; Set read bit in EECR
in r1,$1D ; Read EEPROM data
Words: 1 (2 bytes)
Cycles: 2
1001 1010 AAAA Abbb
I T H S V N Z C
– – – – – – – –

0856C–09/01
SBIC – Skip if Bit in I/O Register is Cleared
Description:
This instruction tests a single bit in an I/O register and skips the next instruction if the bit is cleared. This instruction oper-
ates on the lower 32 I/O registers – addresses 0-31.
Operation:
(i) If I/O(A,b) = 0 then PC ← PC + 2 (or 3) else PC ← PC + 1
(i) SBIC A,b 0 ≤ A ≤ 31, 0 ≤ b ≤ 7 PC ← PC + 1, Condition false - no skip
16-bit Opcode:
Example:
e2wait: sbic $1C,1 ; Skip next inst. if EEWE cleared
rjmp e2wait ; EEPROM write not finished
Words: 1 (2 bytes)
1001 1001 AAAA Abbb
I T H S V N Z C
– – – – – – – –

119
AVR Instruction Set
0856C–09/01
SBIS – Skip if Bit in I/O Register is Set
Description:
This instruction tests a single bit in an I/O register and skips the next instruction if the bit is set. This instruction operates on
the lower 32 I/O registers – addresses 0-31.
Operation:
(i) If I/O(A,b) = 1 then PC ← PC + 2 (or 3) else PC ← PC + 1
(i) SBIS A,b 0 ≤ A ≤ 31, 0 ≤ b ≤ 7 PC ← PC + 1, Condition false - no skip
16-bit Opcode:
Example:
waitset: sbis $10,0 ; Skip next inst. if bit 0 in Port D set
rjmp waitset ; Bit not set
Words: 1 (2 bytes)
1001 1011 AAAA Abbb
I T H S V N Z C
– – – – – – – –

0856C–09/01
SBIW – Subtract Immediate from Word
Description:
Subtracts an immediate value (0-63) from a register pair and places the result in the register pair. This instruction operates
on the upper four register pairs, and is well suited for operations on the pointer registers.
Operation:
(i) Rd+1:Rd ← Rd+1:Rd - K
(i) SBIW Rd+1:Rd,K d ∈ {24,26,28,30}, 0 ≤ K ≤ 63 PC ← PC + 1
16-bit Opcode:
V: Rdh7 •R15
N: R15
Z: R15• R14 •R13 •R12 •R11• R10• R9• R8• R7• R6 •R5• R4• R3 •R2• R1• R0
C: R15• Rdh7
R (Result) equals Rdh:Rdl after the operation (Rdh7-Rdh0 = R15-R8, Rdl7-Rdl0=R7-R0).
Example:
sbiw r25:r24,1 ; Subtract 1 from r25:r24
sbiw YH:YL,63 ; Subtract 63 from the Y pointer(r29:r28)
Words: 1 (2 bytes)
Cycles: 2
1001 0111 KKdd KKKK
I T H S V N Z C
– – – ⇔ ⇔ ⇔ ⇔ ⇔

121
AVR Instruction Set
0856C–09/01
SBR – Set Bits in Register
Description:
Sets specified bits in register Rd. Performs the logical ORI between the contents of register Rd and a constant mask K and
places the result in the destination register Rd.
Operation:
(i) Rd ← Rd v K
(i) SBR Rd,K 16 ≤ d ≤ 31, 0 ≤ K ≤ 255 PC ← PC + 1
16-bit Opcode:
V: 0
Cleared
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
Example:
sbr r16,3 ; Set bits 0 and 1 in r16
sbr r17,$F0 ; Set 4 MSB in r17
Words: 1 (2 bytes)
Cycles: 1
0110 KKKK dddd KKKK
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ –

0856C–09/01
SBRC – Skip if Bit in Register is Cleared
Description:
This instruction tests a single bit in a register and skips the next instruction if the bit is cleared.
Operation:
(i) If Rr(b) = 0 then PC ← PC + 2 (or 3) else PC ← PC + 1
(i) SBRC Rr,b 0 ≤ r ≤ 31, 0 ≤ b ≤ 7 PC ← PC + 1, Condition false - no skip
16-bit Opcode:
Example:
sbrc r0,7 ; Skip if bit 7 in r0 cleared
sub r0,r1 ; Only executed if bit 7 in r0 not cleared
Words: 1 (2 bytes)
1111 110r rrrr 0bbb
I T H S V N Z C
– – – – – – – –

123
AVR Instruction Set
0856C–09/01
SBRS – Skip if Bit in Register is Set
Description:
This instruction tests a single bit in a register and skips the next instruction if the bit is set.
Operation:
(i) If Rr(b) = 1 then PC ← PC + 2 (or 3) else PC ← PC + 1
(i) SBRS Rr,b 0 ≤ r ≤ 31, 0 ≤ b ≤ 7 PC ← PC + 1, Condition false - no skip
16-bit Opcode:
Example:
sbrs r0,7 ; Skip if bit 7 in r0 set
neg r0 ; Only executed if bit 7 in r0 not set
Words: 1 (2 bytes)
1111 111r rrrr 0bbb
I T H S V N Z C
– – – – – – – –

0856C–09/01
SEC – Set Carry Flag
Description:
Sets the Carry flag (C) in SREG (status register).
Operation:
(i) C ← 1
(i) SEC None PC ← PC + 1
16-bit Opcode:
C: 1
Carry flag set
Example:
sec ; Set carry flag
adc r0,r1 ; r0=r0+r1+1
Words: 1 (2 bytes)
Cycles: 1
1001 0100 0000 1000
I T H S V N Z C
– – – – – – – 1

125
AVR Instruction Set
0856C–09/01
SEH – Set Half Carry Flag
Description:
Sets the Half Carry (H) in SREG (status register).
Operation:
(i) H ← 1
(i) SEH None PC ← PC + 1
16-bit Opcode:
H: 1
Half Carry flag set
Example:
seh ; Set Half Carry flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 0101 1000
I T H S V N Z C
– – 1 – – – – –

0856C–09/01
SEI – Set Global Interrupt Flag
Description:
Sets the Global Interrupt flag (I) in SREG (status register). The instruction following SEI will be executed before any pend-
ing interrupts.
Operation:
(i) I ← 1
(i) SEI None PC ← PC + 1
16-bit Opcode:
I: 1
Global Interrupt flag set
Example:
sei ; set global interrupt enable
sleep ; enter sleep, waiting for interrupt
; note: will enter sleep before any pending interrupt(s)
Words: 1 (2 bytes)
Cycles: 1
1001 0100 0111 1000
I T H S V N Z C
1 – – – – – – –

127
AVR Instruction Set
0856C–09/01
SEN – Set Negative Flag
Description:
Sets the Negative flag (N) in SREG (status register).
Operation:
(i) N ← 1
(i) SEN None PC ← PC + 1
16-bit Opcode:
N: 1
Negative flag set
Example:
sen ; Set negative flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 0010 1000
I T H S V N Z C
– – – – – 1 – –

0856C–09/01
SER – Set all Bits in Register
Description:
Loads $FF directly to register Rd.
Operation:
(i) Rd ← $FF
(i) SER Rd 16 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
Example:
clr r16 ; Clear r16
ser r17 ; Set r17
nop ; Delay (do nothing)
Words: 1 (2 bytes)
Cycles: 1
1110 1111 dddd 1111
I T H S V N Z C
– – – – – – – –

129
AVR Instruction Set
0856C–09/01
SES – Set Signed Flag
Description:
Sets the Signed flag (S) in SREG (status register).
Operation:
(i) S ← 1
(i) SES None PC ← PC + 1
16-bit Opcode:
S: 1
Signed flag set
Example:
ses ; Set negative flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 0100 1000
I T H S V N Z C
– – – 1 – – – –

0856C–09/01
SET – Set T Flag
Description:
Sets the T flag in SREG (status register).
Operation:
(i) T ← 1
(i) SET None PC ← PC + 1
16-bit Opcode:
T: 1
T flag set
Example:
set ; Set T flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 0110 1000
I T H S V N Z C
– 1 – – – – – –

131
AVR Instruction Set
0856C–09/01
SEV – Set Overflow Flag
Description:
Sets the Overflow flag (V) in SREG (status register).
Operation:
(i) V ← 1
(i) SEV None PC ← PC + 1
16-bit Opcode:
V: 1
Overflow flag set
Example:
sev ; Set overflow flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 0011 1000
I T H S V N Z C
– – – – 1 – – –

0856C–09/01
SEZ – Set Zero Flag
Description:
Sets the Zero flag (Z) in SREG (status register).
Operation:
(i) Z ← 1
(i) SEZ None PC ← PC + 1
16-bit Opcode:
Z: 1
Zero flag set
Example:
sez ; Set zero flag
Words: 1 (2 bytes)
Cycles: 1
1001 0100 0001 1000
I T H S V N Z C
– – – – – – 1 –

133
AVR Instruction Set
0856C–09/01
SLEEP
Description:
This instruction sets the circuit in sleep mode defined by the MCU control register.
Operation:
Refer to the device documentation for detailed description of SLEEP usage.
SLEEP None PC ← PC + 1
16-bit Opcode:
Example:
ldi r16,(1<<SE) ; Enable sleep mode
out MCUCR, r16
sleep ; Put MCU in sleep mode
Words: 1 (2 bytes)
Cycles: 1
1001 0101 1000 1000
I T H S V N Z C
– – – – – – – –

0856C–09/01
SPM – Store Program Memory
Description:
SPM can be used to erase a page in the program memory, to write a page in the program memory (that is already erased),
and to set boot loader lock bits. In some devices, the program memory can be written one word at a time, in other devices
an entire page can be programmed simultaneously after first filling a temporary page buffer. In all cases, the program mem-
ory must be erased one page at a time. When erasing the program memory, the RAMPZ and Z register are used as page
address. When writing the program memory, the RAMPZ and Z register are used as page or word address, and the R1:R0
register pair is used as data(1)
. When setting the boot loader lock bits, the R1:R0 register pair is used as data. Refer to the
device documentation for detailed description of SPM usage. This instruction can address the entire program memory.
Note: 1. R1 determines the instruction high byte, and R0 determines the instruction low byte.
Operation: Comment:
(i) (RAMPZ:Z) ←=$ffff Erase program memory page
(ii) (RAMPZ:Z) ←=R1:R0 Write program memory word
(iii) (RAMPZ:Z) ←=R1:R0 Write temporary page buffer
(iv) (RAMPZ:Z) ←=TEMP Write temporary page buffer to program memory
(v) BLBITS ←=R1:R0 Set boot loader lock bits
(i)-(v) SPM None PC ← PC + 1
16-bit Opcode:
Example:
;This example shows SPM write of one page for devices with page write
;- the routine writes one page of data from RAM to Flash
; the first data location in RAM is pointed to by the Y pointer
; the first data location in Flash is pointed to by the Z pointer
;- error handling is not included
;- the routine must be placed inside the boot space
; (at least the do_spm sub routine)
;- registers used: r0, r1, temp1, temp2, looplo, loophi, spmcrval
; (temp1, temp2, looplo, loophi, spmcrval must be defined by the user)
; storing and restoring of registers is not included in the routine
; register usage can be optimized at the expense of code size
.equPAGESIZEB = PAGESIZE*2;PAGESIZEB is page size in BYTES, not words
.org SMALLBOOTSTART
write_page:
;page erase
1001 0101 1110 1000
I T H S V N Z C
– – – – – – – –

135
AVR Instruction Set
0856C–09/01
ldispmcrval, (1<<PGERS) + (1<<SPMEN)
calldo_spm
;transfer data from RAM to Flash page buffer
ldilooplo, low(PAGESIZEB);init loop variable
ldiloophi, high(PAGESIZEB);not required for PAGESIZEB<=256
wrloop:ldr0, Y+
ldr1, Y+
ldispmcrval, (1<<SPMEN)
calldo_spm
adiwZH:ZL, 2
sbiwloophi:looplo, 2;use subi for PAGESIZEB<=256
brnewrloop
;execute page write
subiZL, low(PAGESIZEB);restore pointer
sbciZH, high(PAGESIZEB);not required for PAGESIZEB<=256
ldispmcrval, (1<<PGWRT) + (1<<SPMEN)
calldo_spm
;read back and check, optional
ldilooplo, low(PAGESIZEB);init loop variable
ldiloophi, high(PAGESIZEB);not required for PAGESIZEB<=256
subiYL, low(PAGESIZEB);restore pointer
sbciYH, high(PAGESIZEB)
rdloop:lpmr0, Z+
ldr1, Y+
cpser0, r1
jmperror
sbiwloophi:looplo, 2;use subi for PAGESIZEB<=256
brnerdloop
;return
ret
do_spm:
;input: spmcrval determines SPM action
;disable interrupts if enabled, store status
intemp2, SREG
cli
;check for previous SPM complete
wait:intemp1, SPMCR
sbrctemp1, SPMEN
rjmpwait
;SPM timed sequence
outSPMCR, spmcrval
spm
;restore SREG (to enable interrupts if originally enabled)
outSREG, temp2
ret

0856C–09/01
Words: 1 (2 bytes)
Cycles: depends on the operation

137
AVR Instruction Set
0856C–09/01
ST – Store Indirect From Register to Data Space using Index X
Description:
Stores one byte indirect from a register to data space. For parts with SRAM, the data space consists of the register file, I/O
The data location is pointed to by the X (16 bits) pointer register in the register file. Memory access is limited to the current
data segment of 64K bytes. To access another data segment in devices with more than 64K bytes data space, the RAMPX
The X pointer register can either be left unchanged by the operation, or it can be post-incremented or pre-decremented.
These features are especially suited for accessing arrays, tables, and stack pointer usage of the X pointer register. Note
that only the low byte of the X pointer is updated in devices with no more than 256 bytes data space. For such devices, the
high byte of the pointer is not used by this instruction and can be used for other purposes. The RAMPX register in the I/O
area is updated in parts with more than 64K bytes data space or more than 64K bytes program memory, and the increment/
decrement is added to the entire 24-bit address on such devices.
ST X+, r26
ST X+, r27
ST -X, r26
ST -X, r27
Using the X pointer:
Operation: Comment:
(i) (X) ← Rr X: Unchanged
(ii) (X) ← Rr X ← X+1 X: Post incremented
(iii) X ← X - 1 (X) ← Rr X: Pre decremented
(i) ST X, Rr 0 ≤ r ≤ 31 PC ← PC + 1
(ii) ST X+, Rr 0 ≤ r ≤ 31 PC ← PC + 1
(iii) ST -X, Rr 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode :
(i) 1001 001r rrrr 1100
(ii) 1001 001r rrrr 1101
(iii) 1001 001r rrrr 1110
I T H S V N Z C
– – – – – – – –

0856C–09/01
Example:
clr r27 ; Clear X high byte
st X+,r0 ; Store r0 in data space loc. $60(X post inc)
st X,r1 ; Store r1 in data space loc. $61
st X,r2 ; Store r2 in data space loc. $63
st -X,r3 ; Store r3 in data space loc. $62(X pre dec)
Words: 1 (2 bytes)
Cycles: 2

139
AVR Instruction Set
0856C–09/01
ST (STD) – Store Indirect From Register to Data Space using Index Y
Description:
Stores one byte indirect with or without displacement from a register to data space. For parts with SRAM, the data space
consists of the register file, I/O memory and internal SRAM (and external SRAM if applicable). For parts without SRAM, the
data space consists of the register file only. The EEPROM has a separate address space.
The data location is pointed to by the Y (16 bits) pointer register in the register file. Memory access is limited to the current
data segment of 64K bytes. To access another data segment in devices with more than 64K bytes data space, the RAMPY
The Y pointer register can either be left unchanged by the operation, or it can be post-incremented or pre-decremented.
These features are especially suited for accessing arrays, tables, and stack pointer usage of the Y pointer register. Note
that only the low byte of the Y pointer is updated in devices with no more than 256 bytes data space. For such devices, the
high byte of the pointer is not used by this instruction and can be used for other purposes. The RAMPY register in the I/O
area is updated in parts with more than 64K bytes data space or more than 64K bytes program memory, and the increment/
decrement/displacement is added to the entire 24-bit address on such devices.
ST Y+, r28
ST Y+, r29
ST -Y, r28
ST -Y, r29
Using the Y pointer:
Operation: Comment:
(i) (Y) ← Rr Y: Unchanged
(ii) (Y) ← Rr Y ← Y+1 Y: Post incremented
(iii) Y ← Y - 1 (Y) ← Rr Y: Pre decremented
(iiii) (Y+q) ← Rr Y: Unchanged, q: Displacement
(i) ST Y, Rr 0 ≤ r ≤ 31 PC ← PC + 1
(ii) ST Y+, Rr 0 ≤ r ≤ 31 PC ← PC + 1
(iii) ST -Y, Rr 0 ≤ r ≤ 31 PC ← PC + 1
(iiii) STD Y+q, Rr 0 ≤ r ≤ 31, 0 ≤ q ≤ 63 PC ← PC + 1
16-bit Opcode:
(i) 1000 001r rrrr 1000
(ii) 1001 001r rrrr 1001
(iii) 1001 001r rrrr 1010
(iiii) 10q0 qq1r rrrr 1qqq

0856C–09/01
Example:
clr r29 ; Clear Y high byte
st Y+,r0 ; Store r0 in data space loc. $60(Y post inc)
st Y,r1 ; Store r1 in data space loc. $61
st Y,r2 ; Store r2 in data space loc. $63
st -Y,r3 ; Store r3 in data space loc. $62(Y pre dec)
std Y+2,r4 ; Store r4 in data space loc. $64
Words: 1 (2 bytes)
Cycles: 2
I T H S V N Z C
– – – – – – – –

141
AVR Instruction Set
0856C–09/01
ST (STD) – Store Indirect From Register to Data Space using Index Z
Description:
Stores one byte indirect with or without displacement from a register to data space. For parts with SRAM, the data space
consists of the register file, I/O memory and internal SRAM (and external SRAM if applicable). For parts without SRAM, the
data space consists of the register file only. The EEPROM has a separate address space.
The data location is pointed to by the Z (16 bits) pointer register in the register file. Memory access is limited to the current
data segment of 64K bytes. To access another data segment in devices with more than 64K bytes data space, the RAMPZ
The Z pointer register can either be left unchanged by the operation, or it can be post-incremented or pre-decremented.
These features are especially suited for stack pointer usage of the Z pointer register, however because the Z pointer regis-
ter can be used for indirect subroutine calls, indirect jumps and table lookup, it is often more convenient to use the X or Y
pointer as a dedicated stack pointer. Note that only the low byte of the Z pointer is updated in devices with no more than
256 bytes data space. For such devices, the high byte of the pointer is not used by this instruction and can be used for
other purposes. The RAMPZ register in the I/O area is updated in parts with more than 64K bytes data space or more than
64K bytes program memory, and the increment/decrement/displacement is added to the entire 24-bit address on such
devices.
ST Z+, r30
ST Z+, r31
ST -Z, r30
ST -Z, r31
Using the Z pointer:
Operation: Comment:
(i) (Z) ←Rr Z: Unchanged
(ii) (Z) ← Rr Z ← Z+1 Z: Post incremented
(iii) Z ← Z - 1 (Z) ← Rr Z: Pre decremented
(iiii) (Z+q) ← Rr Z: Unchanged, q: Displacement
(i) ST Z, Rr 0 ≤ r ≤ 31 PC ← PC + 1
(ii) ST Z+, Rr 0 ≤ r ≤ 31 PC ← PC + 1
(iii) ST -Z, Rr 0 ≤ r ≤ 31 PC ← PC + 1
(iiii) STD Z+q, Rr 0 ≤ r ≤ 31, 0 ≤ q ≤ 63 PC ← PC + 1

0856C–09/01
16-bit Opcode :
Example:
st Z+,r0 ; Store r0 in data space loc. $60(Z post inc)
st Z,r1 ; Store r1 in data space loc. $61
st Z,r2 ; Store r2 in data space loc. $63
st -Z,r3 ; Store r3 in data space loc. $62(Z pre dec)
std Z+2,r4 ; Store r4 in data space loc. $64
Words: 1 (2 bytes)
Cycles: 2
(i) 1000 001r rrrr 0000
(ii) 1001 001r rrrr 0001
(iii) 1001 001r rrrr 0010
(iiii) 10q0 qq1r rrrr 0qqq
I T H S V N Z C
– – – – – – – –

143
AVR Instruction Set
0856C–09/01
STS – Store Direct to Data Space
Description:
Stores one byte from a Register to the data space. For parts with SRAM, the data space consists of the register file, I/O
A 16-bit address must be supplied. Memory access is limited to the current data segment of 64K bytes. The STS instruction
uses the RAMPD register to access memory above 64K bytes. To access another data segment in devices with more than
64K bytes data space, the RAMPD in register in the I/O area has to be changed.
Operation:
(i) (k) ← Rr
(i) STS k,Rr 0 ≤ r ≤ 31, 0 ≤ k ≤ 65535 PC ← PC + 2
32-bit Opcode:
Example:
lds r2,$FF00 ; Load r2 with the contents of data space location $FF00
add r2,r1 ; add r1 to r2
sts $FF00,r2 ; Write back
Words: 2 (4 bytes)
Cycles: 2
1001 001d dddd 0000
kkkk kkkk kkkk kkkk
I T H S V N Z C
– – – – – – – –

0856C–09/01
SUB – Subtract without Carry
Description:
Subtracts two registers and places the result in the destination register Rd.
Operation:
(i) Rd ← Rd - Rr
(i) SUB Rd,Rr 0 ≤ d ≤ 31, 0 ≤ r ≤ 31 PC ← PC + 1
16-bit Opcode:
H: Rd3• Rr3 +Rr3 •R3 +R3• Rd3
V: Rd7• Rr7 •R7 +Rd7 •Rr7• R7
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
C: Rd7• Rr7 +Rr7 •R7 +R7• Rd7
Set if the absolute value of the contents of Rr is larger than the absolute value of Rd; cleared otherwise.
Example:
brne noteq ; Branch if r12<>r13
...
Words: 1 (2 bytes)
Cycles: 1
0001 10rd dddd rrrr
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

145
AVR Instruction Set
0856C–09/01
SUBI – Subtract Immediate
Description:
Subtracts a register and a constant and places the result in the destination register Rd. This instruction is working on Reg-
ister R16 to R31 and is very well suited for operations on the X, Y and Z pointers.
Operation:
(i) Rd ← Rd - K
(i) SUBI Rd,K 16 ≤ d ≤ 31, 0 ≤ K ≤ 255 PC ← PC + 1
16-bit Opcode:
H: Rd3• K3+K3 •R3 +R3 •Rd3
V: Rd7• K7 •R7 +Rd7• K7 •R7
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
C: Rd7• K7 +K7 •R7 +R7• Rd7
Example:
subi r22,$11 ; Subtract $11 from r22
brne noteq ; Branch if r22<>$11
...
Words: 1 (2 bytes)
Cycles: 1
0101 KKKK dddd KKKK
I T H S V N Z C
– – ⇔ ⇔ ⇔ ⇔ ⇔ ⇔

0856C–09/01
SWAP – Swap Nibbles
Description:
Swaps high and low nibbles in a register.
Operation:
(i) R(7:4) ← Rd(3:0), R(3:0) ← Rd(7:4)
(i) SWAP Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode:
Example:
inc r1 ; Increment r1
swap r1 ; Swap high and low nibble of r1
inc r1 ; Increment high nibble of r1
swap r1 ; Swap back
Words: 1 (2 bytes)
Cycles: 1
1001 010d dddd 0010
I T H S V N Z C
– – – – – – – –

147
AVR Instruction Set
0856C–09/01
TST – Test for Zero or Minus
Description:
Tests if a register is zero or negative. Performs a logical AND between a register and itself. The register will remain
unchanged.
Operation:
(i) Rd ← Rd • Rd
(i) TST Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode: (see AND Rd, Rd)
V: 0
Cleared
N: R7
Z: R7• R6 •R5• R4• R3 •R2• R1• R0
R (Result) equals Rd.
Example:
tst r0 ; Test r0
breq zero ; Branch if r0=0
...
zero: nop ; Branch destination (do nothing)
Words: 1 (2 bytes)
Cycles: 1
0010 00dd dddd dddd
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ –

0856C–09/01
WDR – Watchdog Reset
Description:
This instruction resets the Watchdog Timer. This instruction must be executed within a limited time given by the WD pres-
caler. See the Watchdog Timer hardware specification.
Operation:
(i) WD timer restart.
(i) WDR None PC ← PC + 1
16-bit Opcode:
Example:
wdr ; Reset watchdog timer
Words: 1 (2 bytes)
Cycles: 1
1001 0101 1010 1000
I T H S V N Z C
– – – – – – – –

© Atmel Corporation 2001.
Atmel Corporation makes no warranty for the use of its products, other than those expressly contained in the Company’s standard warranty
which is detailed in Atmel’s Terms and Conditions located on the Company’s web site. The Company assumes no responsibility for any errors
which may appear in this document, reserves the right to change devices or specifications detailed herein at any time without notice, and does
not make any commitment to update the information contained herein. No licenses to patents or other intellectual property of Atmel are granted
by the Company in connection with the sale of Atmel products, expressly or by implication. Atmel’s products are not authorized for use as critical
components in life support devices or systems.
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0856C–09/01
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