8085 Architecture.pptx420.pptx

Group: B.Sc. III Year
Subject: Electronics
Semester: 5
Paper : 5
w.e.f. 2018 - 19 ADMITTED BATCH
Title of the paper: Microprocessor (Intel 8085)
P.R. GOVERNMENT COLLEGE (A), KAKINADA

Topic : Architecture of 8085 Microprocessor

The internal architecture of the 8085 microprocessor
determines how and what operations can be performed with the data
operations are,
 Store 8-bit data.
 Perform arithmetic and logical operations.
 Test for conditions.
 Sequence the execution of instructions.
 Store data temporarily in read write memory called stack.

The 8085 has 6 general purpose registers to store 8-bit data during
program execution.
These 6 registers are identified as B, C, D, E, H and L.
They can be combined as register pairs BC, DE and HL to perform
some 16-bit operations.
These registers are programmable. It can use to load or transfer data
from the registers by using instructions.
Registers

 The accumulator (A) is an 8-bit register that is part of ALU.
 It is used to store 8-bit data and to perform ALU operations.
 The result of an operation is stored in Accumulator.
 The Accumulator is identified as register A.
 The data on which operations is to be performed is operand. One
of the operands must be Accumulator.
Accumulator

This 16-bit register deals with sequencing the execution of instructions.
This register is a memory pointer. Memory locations have 16-bit address.
The microprocessor uses this register to sequence the execution of the
instructions.
The function of the program counter is to point to the memory address
from which the next byte is to be fetched.
When a byte is being fetched, the program counter is automatically
incremented by one to point to the next memory location.
Program Counter (PC)

The stack pointer is also a 16-bit register, used as a memory
pointer.
It points to a memory location in R/W memory, called stack.
The beginning of the stack is defined by loading 16- bit address in
the stack pointer.
Stack Pointer (SP)

 This unit synchronizes all the microprocessor operations with
the clock and generates the control signal necessary for
communication between the microprocessor and peripherals.
 The control signals are similar to a sync pulse in an
oscilloscope. The 𝑅𝐷 and 𝑊𝑅 signals are sync pulses
indicating the availability of data on the data bus.
Timing and control unit

 The instruction register and decoder are part of the ALU.
 When an instruction is fetched from the memory it is loaded in to
the instruction register.
 The decoder decodes the instruction and establishes the sequence
of events to follow.
 The instruction register is not programmable and cannot be
accessed by any instruction.
Instruction register and Decoder

 There are two additional registers called temporary registers W and
Z, which are included in the register array along with
programmable registers namely B, C, D, E, H, L, SP and PC.
 These registers are used to hold 8-bit data during the execution of
instructions. However, they are used internally by microprocessor,
they are available to the program.
Register Array

 This unit is used to select a register out of all the available registers.
 This unit behaves as Multiplexer (MUX) when data going from the
register to the internal data bus.
 It behaves as Demultiplexer(DEMUX) when data is coming to a
register from the internal data bus of the processor.
 The register select will behave as the function of selection lines at
the Mux / Demux.
MUX / DEMUX unit

This is an 8-bit unidirectional buffer.
It is used to drive external high order address bus (A15 – A8).
It is also used to tri-state the high order address bus under certain
conditions such as reset, hold, halt and when address lines are not
in use.
Address Buffer

This is an 8-bit bi-directional buffer.
It is used to drive multiplexed address/data bus. i.e., low order
address bus (A7-A0) and data bus (D7-D0).
It is also to tri-state the multiplexed address/data bus under certain
conditions such as reset, hold, halt and when the bus is not in use.
Address / Data Buffer

 This 16-bit register is used to increment or decrement
the contents of program counter or stack pointer as part
of execution of instructions related to them.
Incrementer/Decrementer address latch

 The ALU includes five flip-flops, which are set (or) reset after an
operation according to data condition of the result in the
accumulator and other registers.
 They are called Zero (Z), Carry (CY), Sign (S), Parity (P) and
Auxiliary Carry (AC) flags.
 Their bit positions in the flag register are shown in Fig. The
microprocessor uses these flags to test data conditions.
Flag register

8085 Architecture.pptx420.pptx

8085 Architecture.pptx420.pptx

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