8051,chapter2

8051 Microcontroller
BY
Amruta Chintawar
Sunday, March 28, 2021 1
MCA/TE/V BY
AMRUTA CHINTAWAR

Topics Covered
• Addressing modes
• Instruction Set
• Assembler Directives
• Programming
Sunday, March 28, 2021 MCA/TE/V BY AMRUTA CHINTAWAR 2

Addressing Modes
• Ways by which source and destination
operands(data) are specified in an instruction
is called Addressing mode
• Instruction may contain 1,2 or no operand
• 8051 has 6 address spaces
– Bank register(R0-R7)
– Accumulator
– Internal RAM(00-7F & SFRs)
– External data RAM
– Program ROM
– Immediate data

Steps to Run the Program

Addressing Modes
• Immediate
• Register
• Direct
• Register Indirect
• Index addressing –Code access
Data access

Immediate addressing
• Source operand is a Constant
• When instruction is assembled,operand
comes immediately after opcode
• Immediate data is preceded by “#”
• Used to load any register including DPTR

Immediate addressing
Sunday, March 28, 2021 MCA/TE/V 7
Eg:
MOV A,#20H
MOV R0,#20H
MOV DPTR,#2000H
MCA/TE/V BY AMRUTA CHINTAWAR

Register Addressing Modes
• It uses register to hold data to be
manipulated
Eg:
MOV A,R0
MOV R7,A
ADD A,R3

Direct Addressing Mode
• The data is in RAM memory location whose
address is known and which is a part of
instruction
• Address follows the opcode
Eg:
MOV A,0F0H
MOV R0,50H
MOV 50H,A

Register Indirect Addressing Mode
• Register is used as a pointer to the data
• Only R0 and R1 are used to hold address if
data is inside CPU
• In other words R2-R7 are not used to hold
RAM address
• External RAM register DPTR is used
• Register are preceded by “@”
Eg: MOV A,@R0
MOV @R1,B

Index Addressing Mode
• It is widely used in accessing data elements of
Look-up table entries located in program ROM
space of 8051
• The 16-dptr and register “A” are used to form
data element stored in On-chip ROM
• Because the data elements are stored in
program space ROM of 8051,it uses
instruction MOVC instead of MOV
• In this instruction the content of A are added
to DPTR to form the 16-bit address of the
needed data

Index Addressing Mode
Eg:
MOV A,@A+DPTR

Instruction Set
• Data Transfer
• Arithmetic
• Logical
• Branching and Looping
• Bit Control
– @Ri implies contents of memory location pointed
to by R0 or R1
– Rn refers to registers R0-R7 of the currently
selected register bank

Data Transfer
• These instructions are used to transfer data
from source operand to destination operand
• Data transfer can be done between
– Internal RAM location and an SFR location without
going through the accumulator
– Internal and external RAM by using indirect
addressing
– The upper 128 bytes of data RAM are accessed
only by indirect addressing
– SFRs are accessed only by direct addressing

Data Transfer
Mnemonic Description
MOV @Ri, direct [@Ri] = [direct]
MOV @Ri, #data [@Ri] = immediate data
MOV DPTR, #data 16 [DPTR] = immediate data
MOVC A,@A+DPTR A = Code byte from [@A+DPTR]
MOVC A,@A+PC A = Code byte from [@A+PC]
MOVX A,@Ri A = Data byte from external ram [@Ri]
MOVX A,@DPTR A = Data byte from external ram [@DPTR]
MOVX @Ri, A External[@Ri] = A
MOVX @DPTR,A External[@DPTR] = A
PUSH direct, Push into stack
POP direct Pop from stack
XCH A,Rn A = [Rn], [Rn] = A
XCH A, direct A = [direct], [direct] = A
XCH A, @Ri A = [@Rn], [@Rn] = A
XCHD A,@Ri Exchange low order digits

Arithmetic
• Instruction are used to perform various
mathematical operations like addition,
subtraction, division and Multiplication
• The appropriate status bits in the PSW are set
when specific conditions are met

Arithmetic

Logical
• Instruction are used to perform various
bitwise operation like ANDing Oring…

Logical

Boolean Variable
• Perform single bit operations
• The operations include set, clear, and, or and
complement instructions
• Also included are bit–level moves or
conditional jump instructions
• All bit accesses use direct addressing

Boolean Variable
CLR C Clear C
CLR bit Clear direct bit
SETB C Set C
SETB bit Set direct bit
CPL C Complement c
CPL bit Complement direct bit
ANL C,bit AND bit with C
ANL C,/bit AND NOT bit with C
ORL C,bit OR bit with C
ORL C,/bit OR NOT bit with C
MOV C,bit MOV bit to C
MOV bit,C MOV C to bit
JC rel Jump if C set
JNC rel Jump if C not set
JB bit,rel Jump if specified bit set
JNB bit,rel Jump if specified bit not set
JBC bit,rel if specified bit set then clear it and jump

Branching and Looping
• Instruction are used to perform Branching and
Looping, control the flow of program
execution
• Include various conditional and unconditional
jumps or loop instruction, provide decision
making capabilities before transferring control
to other parts of the program

Branching and Looping
ACALL addr11 Absolute subroutine call
LCALL addr16 Long subroutine call
RET Return from subroutine
RETI Return from interrupt
AJMP addr11 Absolute jump
LJMP addr16 Long jump
SJMP rel Short jump
JMP @A+DPTR Jump indirect
JZ rel Jump if A=0
JNZ rel Jump if A NOT=0
CJNE A,direct,rel
Compare and Jump if Not Equal
CJNE A,#data,rel
CJNE Rn,#data,rel
CJNE @Ri,#data,rel
DJNZ Rn,rel
Decrement and Jump if Not Zero
DJNZ direct,rel
NOP No Operation

Timer Programming
• Load Timer according to amount of delay and
crystal frequency
• Timer can be started by instruction SETB TRx
• On FFFF 0000 timer overflows and set TF=1
• On overflow CLR TRx stop timer
• Its an up counter
• Value to be loaded in Reg is subtracted from
FFFF

Timer Programming

Timer Programming
• To Start Timer
– SETB TRx
– SETB TCON.4/6
– ORA TCON,#10h== 01010000
• To Stop Timer
– CLR TR0
– CLR TCON.4/6
– ANL TCON,#10101111

Timer Programming
Eg:
Q.1 calculate count to generate a delay of 10ms
with a Crystal frequency of 12Mhz
Sol: Timer clock frequency =12/12 = 1Mhz
Timer clock period =1/1Mhz = 1us
Count to generate
10ms delay =10ms/1us = 10000pulses

Timer Programming
• Timer should overflow after 10000d pulses
• Timer sets overflow flag on overflow from FFFF+1 pulse
• As timer is up counter value to be loaded in Timer is
calculated as:
FFFFh=65535d
Count=65535d-10000d+1
= 55536d=2710h
• Higher byte to be loaded in THx(27) and
Lower byte in TLx(10)

Timer Programming
*T/C starts counting from 2710 when it counts
(10000)d pulses the value it reaches is FFFFh
and on next pulse it will overflow to 0000H set
TF bit to 1

Timer Programming
Steps:
• Calculate time period of timer clock pulse
• Timer clock pulses N to generate required
delay
• Count=FFFF-Nh+1
• Load Higher byte to THx and Lower to TLx

Timer Programming
Eg:
Q.2 Generate a delay of 500us using Timer0 in mode
1,having crystal frequency of 12Mhz
Sol:Timer clock frequency=12/12=1Mhz
Timer clock period=1us
Count required =500/1us = 500d (500 pulses for 500us)
Count to be loaded=65535-500+1
= 65036d
= FE0Ch
TH0=FE and TL0=0C

Timer Programming
Configure TMOD to select Timer 0, C/T#=0
Mode 1 (16 bit timer mode) ,M1 M0=01
Its not H/W control, Gate =0
Thus the word to be loaded in TMOD =01h
After loading count Timer need to be started,
TR0=1 in TCON
On overflow TF=1

Timer Programming
MOV TMOD,#01H TIMER0,MODE1
MOV TH0,#0FEH HIGHER BYTE
MOV TL0,#0CH LOWER BYTE
SETB TR0 START TIMER
WAIT:JNB TF0,WAIT CHECK OVERFLOW
CLR TR0
CLR TF0

Timer Programming
Eg:
Q.3 Generate a square wave of 1Khz on port P2.0 using
Timer 1, crystal frequency 11.0592
Sol: Required period =1/1khz = 1ms
=500us ON and 500us OFF
Freq of Timer clock =11.0592/12 mhz
=0.9215Mhz
Time period of Timer = 1/0.9215Mhz
=1.085us

Timer Programming
Count = 500/1.085
=460.8(461)
For 461 count OFF and 461 ON
Count to be loaded =65535-461+1
=65075d
=FE33h
Load FEh in TH1 and 33h TL1

Timer Programming
MOV TMOD,#10H TIMER1,MODE1
L1: MOV TH1,#0FEH HIGHER BYTE
MOV TL1,#33H LOWER BYTE
SETB TR1 START TIMER
WAIT:JNB TF1,WAIT CHECK OVERFLOW
CLR TR1
CLR TF1
CPL P2.0 Invert bit on port
SJMP L1 repeat to generate
continuous square wave

Timer Programming
Eg:
Q.4 Generate a square wave of 10Khz on port P1.0
using Timer 0, crystal frequency 12Mhz (solve for 11.0592)
Sol: Required period =1/10khz = 100us
=50us ON and 50us OFF
Freq of Timer clock =12/12 mhz
=1Mhz
Time period of Timer = 1/1Mhz
=1

Timer Programming
Count = 50/1
=50
For 50 count OFF and 50 ON
Count to be loaded =255-50+1
=206d
=h
Load ?? in TH1 and ?? TL1
*As it is a Continuous pulse program it in Auto
reload Mode

Serial Programming
Transmission
• Set the port in particular mode
• Store the byte in SBUF
• Start Transmission
• Check Complition by checking TI flag
• Repeat the operation for next byte
*if a particular baud rate is given then
load time with the count

Serial Programming
Reception
• Set the port in particular mode
• Enable Reception
• Wait Until data byte is received in SBUF by
checking RI flag
• Read SBUF
• Clear RI
• Repeat if Next byte to be received

Serial Programming
Q.1Write a Program to Transmit ‘55h’
continuosly in mode 0
MOV SCON,#00h
REPEAT:MOV SBUF,#55H
JNB TI,WAIT
CLR TI
SJMP REPEAT
END

Serial Programming
Q.2 Write a program to receive a data byte in
mode 0.send the received byte to Port1
MOV SCON,#00H
ORA SCON,#10H
WAIT :JNB RI,WAIT
MOV A,SBUF
MOV P1,A
CLR RI
HERE: SJMP HERE
END

Serial Programming
Mode 0
• Baud rate is fixed Fosc/12
• Initialize SCON
Mode 1
• UART is designed mainly for this reason
• Frame format is compatible with COM port of PCs
• Transmission and reception rate is set by T1
• T1 is used to generate baud rate
• 11.0592 Mhz is unusual value used to generate
standard baud rates

Serial Programming
Process of generating specific baud rate:
• Crystal frequency/ 12 generate M/C cycle=921.6Khz
• Further / by 32=28800Hz given to timer1
• This value is further divided by an integer in timer 1
to get standard baud rate
Eg: 28800/3=9600
/6 =4800
/24=2400

Serial Programming
Baud rate calculation
• 11.0592(crys osc)/12=921.6
• If SMOD =0 ,921.6/32=28800HzTimer1 clock
to set Baud rate
• If SMOD=1,921.6/16=57600Hz

Serial Programming
Baud rate calculation
Ftick=Foscx2SMOD/(12x32)
• Ftick is further divide by Timer 1, and amount of
division is controlled by count loaded into its
TH1 reg.
Fbaud = Ftick/(256-TH1)
= Foscx2SMOD/12x32x(256-TH1)
To get desired baud rate approprite count to be
loaded in TH1 gien as:
TH1 = 256-{(FoscX2SMOD)/(12X32xFbaud)}

Serial Programming
Some standard baud rates:
Baud rate Count to be loaded
1200 E8
2400 F4
4800 FA
9600 FD

Serial Programming
Steps to transmit and Receive data serially:
• Timer 1 in 8-Bit auto-reload mode
• Load TH1 according to baud rate
• Configure SCON-Mode 1,REN=1 (reception)
• TR1 =1 start Timer 1
• Byte to be transmitted stored in SBUF
• TI and RI for completion of transmission and
reception resp.
• After completion of Trx and Rx TI and RI cleared
manually
• Repeat last three for transmission and for reception last two

Serial Programming
Q.1 Write a Program to Transmit “A” serially at 9600 baud rate
MOV TMOD,#20H //Timer 1,Mode 2
MOV TH1,#0FDH // 9600bps
MOV SCON,#50H //8BIT DATA,1 STOP BIT,REN enabled
SETB TR1 // START TIMER
MOV SBUF,#”A” //A IN SBUF
L1: JNB TI L1 // WAIT TILL TRANSFER
CLR TI // CLEAR TI BEFORE SENDING NEXT BYTE

Serial Programming
Q.1 Write a Program to Transmit “HAPPY” serially at 9600 baud
rate,8- bit dat,1 stop bit
L1:MOV A,#”H” //H IN A
ACALL SEND
---Repeat FOR A,P,P,Y—
SJMP L1
SEND: MOV SBUF,A
L2: JNB TI L2 // WAIT TILL TRANSFER
RET

Serial Programming
Q.1 Write a Program to receive bytes serially at 9600 baud rate,8-
bit dat,1 stop bit simultaneously send received byte to port 2
L1: JNB RI L1 // WAIT TILL RECEPTION
MOV A, SBUF //READ AND SAVE RECEIVED CHARACTER
MOV P2,A //SEND CHARACTER TO PORT 2
SJMP L1 //GO TO RECEIVE NEXT CHARACTER
END

8051,chapter2

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