Microprocessor Fundamentals and Microcomputers

Microprocessor Fundamentals

• The 8085 microprocessor was first introduced in March 1976.
• It's an 8-bit microprocessor with a 16-bit address width, addressing 64KB of memory.
• It has 40 pins and approximately 6500 transistors.
• It requires a +5 volt power supply and operates at 3 MHz.
• The 8085 is chosen for study due to its widespread use, ease of use, and simple architecture.
• This provides an adequate instruction set, enabling students to readily learn fundamental programming concepts.

Microcomputer

• A microcomputer is a programmable machine.
• It consists of three basic subsystems: the microprocessor, memory, and input/output (I/O) devices.
• These components work together to carry out tasks.
• The 8085 microprocessor was introduced in 1976.
• Communications between components occur via a system bus, encompassing a data bus, an address bus, and a control bus.

Microprocessor

• A microprocessor is a multipurpose, programmable, clock-driven, register-based electronic device.
• It retrieves binary instructions from memory.
• It processes binary data according to those instructions.
• It delivers results as output.

Microcontroller

• A microcontroller is a microcomputer built on a single chip.
• It comprises a microprocessor, memory (including program and data memory), input/output (I/O) devices, and extra peripherals, such as analog-to-digital converters and timers.
• Examples include Microchip PIC, Motorola, and ATMEL chips.

Bits, Bytes, and Words

• Computer operations are based on binary digits (bits) - 0 and 1. Electrical voltages represent these bits.
• A byte is composed of eight bits.
• A word is a collection of bits executed in a single operation. Word size varies depending on the microprocessor (8-bit, 16-bit, 32-bit, or 64-bit).
• Memory word size is usually a byte.
• Memory is measured in units like kilobytes (kB), megabytes (MB), gigabytes (GB), and terabytes (TB).

Software

• Software consists of instructions, written in bit patterns, that dictate actions for the microprocessor.
• Software consists of a group of programs.
• Programs set procedures to carry out tasks.
• Binary instructions are challenging to write, hence, assembly-level programming uses English-like words to represent these instructions.
• Both assembly and machine languages are specific to each microprocessor.

Assembly Language

• Assembly language uses symbolic codes (mnemonics) that resemble operations.

Microprocessor Architecture

• A microprocessor internally comprises three main units: the Arithmetic Logic Unit (ALU), the Register Array, and the Control Unit.

ALU

• The Arithmetic Logic Unit (ALU) performs all computational and logical tasks.
• Tasks include addition, subtraction, and logical operations (AND, OR, XOR).

Control Unit

• The control unit governs the microprocessor's operation—which components are activated and the timing sequence—and handles interactions with peripherals (input/output, or I/O).
• This includes synchronization mechanisms, interrupt processes, and the power-up sequence.

Register Array

• A register array holds storage registers.
• These registers are designed for high-speed data storage during program execution.
• General-purpose registers are flexible; programmers can use them any way they need.
• Special-purpose registers have dedicated tasks, such as helping with flag indicators.

Memory

• Microprocessor components essential for storing and accessing data and instructions.
• There are two types:
  • Primary memory (e.g. RAM, ROM)
  • Secondary memory (e.g., hard drives, CDs, USB drives)

RAM

• Random Access Memory (RAM) is comprised of storage registers. Each register utilizes flip-flops to store information bits. Each flip-flop is a memory cell.

ROM

• Read-Only Memory (ROM) permanently stores data using diodes. Diodes can be thought of as registers in this instance.

I/O Devices

• Input/output (I/O) is used by the system to communicate with the outside world.
• Examples of I/O devices include peripherals such as keyboards, mice, scanners, speakers, and monitors.
• Input devices send data from the external world to the processor.
• Output devices send data from the processor to the external world.

8085 Microprocessor

• The 8085 microprocessor is an 8-bit microprocessor with 40 pins.

8085 Microprocessor Buses

• Address Bus (16 pins)
• Data Bus (8 multiplexed pins)
• Control & Status Bus (6 pins)

8085 Microprocessor Power Supply & Frequency

• Vcc (+5V) is the power supply.
• Vss (Ground)
• X1, X2 are pins for the crystal, responsible for system clock frequency (ideally 6 MHz, internally divided to 3 MHz). (Clock output)

8085 Microprocessor Interrupt & Acknowledge Signals

• These enable other devices to interrupt processor execution.

8085 Instruction & Decoder and Timing & Control

• The 8085 instruction decoder interprets instructions and commands the appropriate operation sequence.
• The timing & control unit governs the precise timing and communication among all parts and components of the micro-processor.

8085 Register Array

• These registers store data temporarily during operations.
• Specific registers include the accumulator, temporary register, status register, general-purpose registers, program counter, and stack pointer, and memory-address register.

8085 ALU

• The Arithmetic Logic Unit (ALU) deals with data manipulation operations.

8085 Internal Diagram

• The 8085 includes an ALU, timing and control unit, an instruction register and decoder, and a register array, and serial I/O control.