Instruction Cycle

A program residing in the main memory of a computer contains a sequence of instructions. These instructions executed by the CPU by completing a cycle for each instruction.

In a basic computer, each cycle for instruction consists of the following steps:

  1. Fetch the instruction from memory.
  2. Decode the instruction.
  3. Read the effective address from memory.
  4. Execute the instruction.

Instruction Cycle in COA

Input-Output Configuration

In computer architecture, input-output devices act as an interface between the user and the computer. A Block diagram for the input-output configuration for a basic computer, given below.

Input-Output Configuration in COA

  • The input and output terminals send and receive information respectively.
  • The amount of information transferred through the input unit will always have eight bits.
  • The information generated by the input unit i.e. keyboard is transferred into an input register ‘INPR’.
  • The information for the printer is store in the output register ‘OUTR’.
  • Registers INPR and OUTR communicate with each other serially through AC. But AC works parallel.  
  • The transmitter interface gets the information from the input unit i.e. keyboard and transmits it to INPR serially.
  • The receiver interface receives information from the output register (OUTR) and sends it to the printer serially.

Design of a Basic Computer

A basic computer consists of the following hardware components.

  1. A memory unit with 4096 words and size of each word is 16.
  2. Registers: AC (Accumulator), DR (Data register), IR (Instruction register), PC (Program counter), AR (Address register), TR (Temporary register), SC (Sequence Counter), INPR (Input register), and OUTR (Output register).
  3. Flip-Flops: I, S, E, R, IEN, FGI, and FGO
  4. Two decoders: a 3 x 8 operation decoder and 4 x 16 timing decoder
  5. A 16-bit common bus
  6. Control Logic Gates
  7. The Logic and Adder circuits which are connect with the input of AC.

Note: FGI and FGO are consider as control flip-flops.

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