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EET 252 Unit 8 Computer Basics. Read Floyd, Sections 13-1 to 13-6 (skimming Section 13-3 and pages 739-745). Do Lab #8. Homework #8 and Lab #8 due next week. Quiz next week. Figure 13.1 Basic computer block diagram. Computer Block Diagram.

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eet 252 unit 8 computer basics
EET 252 Unit 8Computer Basics
  • Read Floyd, Sections 13-1 to 13-6 (skimming Section 13-3 and pages 739-745).
  • Do Lab #8.
  • Homework #8 and Lab #8 due next week.
  • Quiz next week.

Computer Block Diagram

The microprocessor or central processing unit (CPU) fetches instructions from memory and executes them.

Memory stores instructions and data until needed by the CPU.

The ports are the I/O connections to the peripherals.

The buses are groups of conductorswith a common purpose.

Peripherals are devices for inputting or outputting information.


Roles of the Microprocessor

  • The microprocessor is the heart of a computer system. It performs the following functions:
    • Fetches instructions from memory.
    • Decodes and executes the instructions. This typically involves:
      • Transferring data to/from memory or I/O devices.
      • Performing arithmetic or logical operations on data.
    • Provides timing and control signals for all other elements in the computer.
    • Responds to interrupts (requests from I/O devices).

Microprocessor Block Diagram

Four blocks are common to all microprocessors. These are:

  • ALU
    • Performs arithmetic and logic operations.
  • Instruction decoder
    • Translates the current instruction into hardware signals for executing the instruction.
  • Register array
    • A group of temporary storage locations within the processor. Some registers have a dedicated special purpose; others are general purpose.
  • Control unit
    • Synchronizes the processing of instructions.


Arithmetic logic unit (ALU)

Instruction decoder

Register array

Control unit


Microprocessor Buses

A bus consists of a set of wires or circuit-board traces over which information moves from one place to another.

The address bus is used by the microprocessor to specify a location in memory or external device.

The data bus transfers data and instruction codes to and from memory and I/O ports.

The control bus coordinates operations and communicates with external devices.


Some Popular Microprocessor Families

  • Dozens of companies design and manufacture microprocessors. Three of the most popular:
    • Intel
      • 4004, 8008, 8051, 8086, 80286, 80386, Pentium, Celeron, Itanium, Xeon, Core 2, …
    • Motorola (Freescale since 2004)
      • 6800, 68HC11, 68000, PowerPC, …
    • Microchip Technology
      • PIC microcontrollers

Microprocessor Datasheet

  • MC6802/6808(datasheet on course website)

Heathkit ET 3400 Microcomputer Trainer

  • Microcomputer system built around Motorola 6802 or 6808 microprocessor.
  • Lets you tap into address bus, data bus, control lines.

Heathkit Trainer: Main Components



Microcomputer System




Data Bus

Control Bus


External Components


Heathkit Trainer: Main Components

Microcomputer System


External Components



Power supply


Heathkit Trainer: Pre-Wired Chip

  • Each Heathkit trainer in this room already has an extra 7400 chip and a few wires installed for you. These will be needed for most of the labs that we do. Please do not remove them.

Heathkit Trainer: Documentation

  • All are taken from Heathkit manual and are posted on course website.
  • Front panel diagrams
  • Block diagram
  • Schematic diagram
  • Detailed explanation of operation

Heathkit Trainer: µP Registers

  • In EET261 & 262 you’ll study internal organization & operation of microprocessors. We just need to know that 6802/6808 has six internal registers that you can access:

Heathkit Trainer: Keypad

  • Seventeen keys; most can be used either to enter a hex digit or to issue a command.

Heathkit Trainer: Address Bus

  • System has a 16-bit address bus connected to 16 output pins on the 6802/6808 microprocessor chip.
  • All bits (A0 through A15) are available at connectors.

Heathkit Trainer: Data Bus

  • System has an 8-bit bi-directional data bus connected to 8 input/output pins on the 6802/6808.
  • All bits (D0 through D7) are available at connectors.

Heathkit Trainer: Control Bus

  • System has 13 timing and control lines available at connectors.
  • Most are connected to pins on the 6802/6808.

Heathkit Trainer: Memory Map

  • Our system has a 16-bit address bus, so addresses can range from $0000 to $FFFF.

Computer Programming

Most programming today is done in high-level languages, which can run on various machines. High-level programs are easier to write and maintain than assembly programs or machine code.

Assembly language is more convenient than machine language. Assembly language is used today for many applications because it executes fast and efficiently. But it must be written for a specific processor.

Early computers were programmed in machine language. Machine language is tedious to write and prone to errors.



  • This program adds two numbers together and stores the result.
  • Third column is the only one the microprocessor understands. The BASIC or Assembly programs must be translated to machine code before being executed.

Computer Programming: Compilers & Assemblers

High-level languages are machine-independent. The source code is translated to machine code by a compiler for the specific processor being used.

High-level language program

(Source program)

Machine language program

(Object program)


Assembly language must be written for the specific processor being used, so the programmer must understand details of how this processor operates. An assembler translates the source code to machine code.

Assembly language program

(Source program)

Machine language program

(Object program)




  • In any computer system, the processor must periodically suspend the program it’s executing to handle data transfers to and from peripheral devices (such as a keyboard or display).
  • Three common ways to do this:
    • Polled I/O
    • Interrupt-driven I/O (Hardware interrupts)
    • Software interrupts
    • (Floyd, p. 746)

Interrupts (Continued)

  • Polled I/O – The processor periodically suspends the current program and checks each peripheral device one at a time to see if it needs service. If it does, the processor executes a service routine to handle the device’s needs.
  • Interrupt driven I/O (Hardware interrupt) – The peripheral device requests service by sending an interrupt request signal. The processor suspends the program currently running, acknowledges the interrupt, executes the service routine, and then returns to its program when the routine is completed.
  • Software interrupt – A software interrupt is issued from software rather than external hardware. When the interrupt is issued, the steps are the same as with a hardware interrupt.

Traditional Handling of I/O Data Transfer

  • Traditionally, data transfers between memory and peripheral devices required the data to pass through the processor.
  • This is not very efficient, compared to….

Direct Memory Access

Direct memory access (DMA) is a data transfer technique in which data is transferred between a peripheral device and memory without involving the CPU. A DMA controller handles the transfer. The transfer is faster using this method.