Intel 8085 Microprocessor Overview

Study Notes

Introduction

The Intel 8085 is an 8-bit microprocessor
It's a complex set of interconnected circuits, all on one chip
Designed for general-purpose use
Popular in education and hobbyist projects

Architecture

Registers: Stores data temporarily
- Accumulator (A): Main register for arithmetic operations
- B, C, D, E: General purpose registers, often used in pairs (BC, DE)
- H, L: General purpose registers, often used as a pointer, for address storage
- Stack Pointer (SP): Keeps track of the top of the stack
- Program Counter (PC): Holds the memory address of the next instruction to be executed.
Arithmetic Logic Unit (ALU): Performs arithmetic and logic operations
Control Unit (CU): Coordinates all operations within the CPU, retrieves instructions, and decodes them into smaller parts.
Input/Output (I/O) Ports: Facilitate data transfer between the microprocessor and peripherals.
Memory: Stores program instructions and data
- Holds both the program and the working data
- Memory can be read from and written to

Instruction Set

MOV (Move): Transfers data between registers or between a register and memory
MVI (Move Immediate): Moves data from an 8-bit immediate operand to a register
LDA/STA (Load/Store Accumulator): Transfers data between the accumulator and memory
ADD/SUB (Add/Subtract): Arithmetic operations on the accumulator
IN/OUT: Input/Output operations
JMP/CALL/RET: Control transfer instructions for program flow (jumps, calls, returns)
JNZ/JZ/JC/JNC: Conditional jumps based on Zero, Carry flags

Addressing Modes

Register Addressing: Operands are located in registers
Immediate Addressing: Operands are directly within the instruction itself
Direct Addressing: Operands are located in memory using the given memory address
Register Indirect Addressing: Use registers as pointers to locations in memory
Base + Displacement Addressing: Allows for addressing memory locations relative to a base register

Flags

Carry Flag: Set if an arithmetic operation results in a carry out
Zero Flag: Set if the result of an operation is zero
Sign Flag: Based on the most significant bit of the result (useful for measuring large numbers)
Parity Flag: Set if the result has an even number of 1s
Auxiliary Carry Flag: Used in BCD (Binary Coded Decimal) arithmetic

Interrupts

Interrupt: A signal that stops the CPU from its current execution to handle a certain event from outside the CPU.
Interrupt Service Routine (ISR): A small program that handles a specific interrupt.
Types of Interrupts: Internal and external interrupts
Interrupt Vectors: Provide the starting address of the ISR for each interrupt

Pin Description

Address Bus: Carries the memory address
Data Bus: Carries the data between the CPU and memory or I/O devices
Control Signals: Various signals, such as RD, WR, control operations

System Design

Often used with RAM (Random Access Memory)
Works with ROM (Read-Only Memory) for storing firmware
May be part of a larger system including input/output devices
Commonly used with hardware such as timers, display interfaces

Applications

Small embedded systems
Industrial control applications
Educational purposes
Hobbyist projects

Limitations

Limited instruction set compared to more modern processors
Less efficient for certain tasks
8-bit architecture might not be sufficient for advanced applications

Description

This quiz covers the basic concepts of the Intel 8085 microprocessor, including its architecture and main components. It is designed for students and hobbyists interested in understanding the functions of various registers, the Arithmetic Logic Unit, and the Control Unit. Test your knowledge on this essential 8-bit microprocessor!