Microprocessor and Microcontroller Architecture Fundamentals

Microprogrammable Systems

A microprogrammable system reads, interprets, and executes sequential instructions contained within a program. These systems are essential for computer applications, mathematical calculations, industrial processes, and electrical apparatus.

Core Components

• Clock: Generates periodic square waves for synchronization.
• Microprocessors: Include the CPU and are used in applications requiring large memory and high-speed processing.
• Microcontrollers: Feature a CPU embedded on a single chip, designed for specific tasks and smaller footprints.
• PLDs (Programmable Logic Devices): Chips that integrate a matrix of logic gates whose functionality can be configured via programming.

Processing Units

The Processing Unit handles arithmetic and logical data from main memory or registers, managing all data transfers.

ALU (Arithmetic Logic Unit)

The ALU is a complex combinational circuit for arithmetic operations:

• ALU 0 Address: Input data comes from the stack.
• ALU 1 Address: One input comes from the RI (Instruction Register) and the other from the Accumulator.
• ALU 2 Addresses: Data comes from two RI registers; the result overwrites the previous value.
• ALU 3 Address: Input data comes from two RI registers, but the result is returned to a different intermediate register.

Internal Memory and Registers

Registers are internal memory components that temporarily store intermediate results of operations, formed by bistable circuits.

• Accumulator: A temporary storage register.
• Status Register: Provides information about the result of the final executed instruction.
• Internal Registers: Used automatically by the microprocessor.
• Subsidiary Registers: Available for the programmer to store data or intermediate results.

Control Unit (UC)

The Control Unit is the most critical part of the microprocessor, governing global functionality by receiving, transforming, and interpreting data.

• Program Counter: Indicates the memory position of the next instruction to execute.
• Instruction Decoder: Translates program instructions stored in memory into internal chip steps.
• Wired Logic: Uses logic gates and counters to generate micro-orders based on inputs and internal status indicators.
• Microprogram: ROM-based memory that stores elementary microprogrammed operations.