Introduction
The Architecture of 8085 Microprocessor is based on an 8-bit data bus and 16-bit address bus. It has a simple instruction set and is well-suited for basic computing tasks and control applications.
The Intel 8085 is an 8-bit microprocessor that was introduced in the mid-1970s. It played a significant role in the early development of microcomputers. The architecture of the 8085 can be divided into different components.
It has the following specifications:
- 8 Bit Data Bus.
- 16 Bit Address Bus
- Address bus can be address upto 64 kB
- A 16 bit SP ( Stack Pointer )
- 16 bit PC ( Program Counter )
- Required +5V supply.
- Much slower in operation, compare to 8086 Microprocessor.
Internal Architecture of 8085 Microprocessor
This is the Architecture of 8085 Microprocessor with many sections. Each section has it’s own function and task by which the whole architecture of 8085 microprocessor works.
Function of Each Block
Below we discuss the function of each and every section of the architecture of 8085 microprocessor.
Timing and Control
The “Brain” of the microprocessor is represented by this box titled “Timing and Control“. This is the sequential machine that we have talked about earlier. Note that the input to the timing and control logic comes from the next “Instruction” of the currently running program.
ALU and Flags
The ALU is the component of the Microprocessor that carries out the Arithmetic (like add, subtract, div etc.) and logical (like AND, OR etc.) on two input operands and produces and output.
Connected to the ALU, there is a set of five flags. These flags are-
- Z or Zero Flag: SET when the result of last operation leaves all zeroes.
- S or Sign Flag: SET when the last operation makes bit-7 (i.e. the most significant bit) of the result 1.
- P or Parity Flag: SET when the last operation leaves an even number of 1-s in the result.
- C or Carry Flag: SET when the last arithmetic operation involves a carry or borrow out of the MSB.
- AC or Auxiliary Carry Flag
| D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
| S | Z | X | AC | X | P | X | C |
Register Bank
There are seven internal 8-bit registers that can be referred to by instructions. They are called B, C, D, E, H, L, and A. The A register is actually the Accumulator that we have talked about in the discussion on ALU.
Accumulator
It is an 8-bit register used to perform arithmetic, logical, I/O & LOAD/STORE operations. It is connected to internal data bus and ALU.
Temporary Register
It is an 8-bit register, which holds the temporary data of Arithmetic and Logical Operation.
Instruction Register and Decoder
It is an 8-bit register. When an instruction is fetched from memory then it is stored in the instruction register and the work of instruction decoder to decode the instruction.
Stack Pointer
In 8085, the stack pointer is a 16 bit register that is used to point into memory representing the stack.
Program Counter
In 8085, the Program Counter is maintained as a 16-bit internal register. Under ‘Normal Control Flow’, the program counter is increments after every byte of the next instruction in ‘fetched’.
Difference between 8-bit and 16-bit Microprocessor
| 8-Bit MP | 16-Bit MP |
|---|---|
| 1. Data bus is 8 bit wide. | 1. Data bus is 16 bit wide. |
| 2. Slower compare to 16-bit. | 2. Faster compare to 16-bit. |
| 3. It’s address bus is 16-bit wide. | 3. It’s address bus is 20-bit wide. |
| 4. Example: Intel 8085. | 4. Example: Intel 8086. |
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