8085 system block diagram

8085 Simple Block diagram

ALU

Control Unit

Description

• ALU– This section performs various functions on Data– ALU can do Aromatic and Logical operations

• Register Array– This section consists of Registers used to store data during

program execution and to store data – The registers are B, C, D, E, H, L,

• Control Unit– This section provides timing and control signals for all the

operations in the microcomputer– This control the flow of data between microprocessor and

peripheral and memory

Memory

• Memory stores data and instructions and provide the information when needed

• Memory consists of ROM and RAM

• ROM Read Only Memory(Store Monitor program or Operating system)

• RAM Random Access Memory(User Memory)

• To execute the program microprocessor reads instructions from memory and performs the computing operations on it in ALU and transfer the data to Output or store the results in Memory

I/O

• It communicates with outside world

• I/O is Input Output it is also known as peripherals

• Input devices transfer data or instruction from outside world to the microprocessor

• Output devices transfer data from microprocessor to outside world

System Bus

• It communication path between microprocessor and peripherals.

• It is a group of wires which carries bits from and to microprocessor.

• Microprocessor communicate with only one peripheral at a time .

• The time signals are provided by control unit of the processor.

Hardware model of 8085

Registers of 8085

Data Bus Address Bus

Accumulator

L (8 bits register)H (8 bits register)

B (8 bits register)

D (8 bits register) E (8 bits register)

C (8 bits register)

Flag Register

Stack Pointer (16 bits)

Program Counter (16 bits)

Registers

• 8085 have six multipurpose 8 bits registers namely B, C, D, E, H,L.

• Accumulator is an 8 bit register it is part of ALU.

• It is used to store 8 bit data to perform arithmetic and logic operations.

• It is also identified as register A.

Flags

• ALU also include five flip flops.

• These are set or rested according to the results in the accumulator.

• These flip flops are showing that whether the data is zero(Z) ,Negative (S), Auxilary Carry or barrow (AC), Carry or barrow (C), Number of one in result (P).

S Z X A X P X C

Program counter and Stack pointer

• These are 16 bits registers used to hold memory addresses.

• Program counter is used to sequence the execution of instructions

• Stack pointer is used as memory pointer.

• It points to the memory location in R/W memory.

8085

Signals and I/O Pins

8085 Microprocessor