Q20Microprocessor and Microcontroller
Question
Draw the architecture diagram of 8085 µP and explain the components.
Answer
A deep internal architectural breakdown of the 8085 microprocessor, detailing the ALU, Register Array, Instruction Decoder, and the massive Timing and Control Unit.
The Intel 8085 is an 8-bit CPU. Its internal silicon architecture is highly optimized for executing sequentially fetched binary instructions. The architecture is logically divided into three massive, interconnected functional blocks: the ALU, the Register Array, and the Timing and Control Unit.
1. The Arithmetic Logic Unit (ALU)
The ALU is the mathematical brain. It is physically engineered with thousands of transistors to execute 8-bit binary addition, subtraction, AND, OR, XOR, and bit-shifting operations. - Accumulator (Register A): An 8-bit register hardwired to one input of the ALU. The result of every ALU operation is permanently stored back here. - Temporary Register: An invisible 8-bit register holding the second operand fetched from memory or another register just before feeding it to the ALU. - Flag Register: A 5-bit status register (Sign, Zero, Aux Carry, Parity, Carry) that alters its state strictly based on the ALU's final mathematical output.
2. The Register Array
This block handles ultra-fast, volatile internal memory storage and address generation. - General Purpose Registers: Six 8-bit registers (B, C, D, E, H, L) available to the programmer. They can be combined into 16-bit pairs (BC, DE, HL) to hold massive 16-bit memory addresses. - Program Counter (PC): A critical 16-bit register that rigorously holds the memory address of the absolute next instruction to be fetched. It automatically increments after every fetch. - Stack Pointer (SP): A 16-bit register explicitly managing the LIFO Stack in external RAM, used heavily during subroutines and interrupts.
3. Instruction Register & Decoder
When an opcode is fetched from RAM, it bypasses the ALU and is securely deposited into the 8-bit Instruction Register. The Instruction Decoder then mathematically analyzes this binary pattern and translates it into a specific sequence of micro-operations.
4. Timing and Control Unit
This massive state machine acts as the central nervous system. Receiving the decoded instructions, it generates a highly complex, flawlessly synchronized sequence of electrical control signals () to aggressively orchestrate the movement of data between the microprocessor, memory, and external I/O ports.