Instruction Cycle
A program stored in a computer's memory is made up of a series of instructions. The processor executes these instructions by following a cycle for each one.
In a basic computer, each instruction cycle includes the following phases:
- Fetch instruction from memory.
- Decode the instruction.
- Read effective address from memory.
- Execute the instruction.
Input - output configuration.
In computer architecture, input-output devices serve as a bridge between the machine and the user.
Data and instructions stored in memory must originate from an input device. The results are then presented to the user through an output device.
The block diagram below illustrates the input-output configuration of a basic computer.
Input - output configuration.
The information transferred will always consist of eight bits of an alphanumeric code.
Information entered via the keyboard is loaded into an input register, known as 'INPR'.
The information intended for the printer is stored in the output register, 'OUTR'.
The INPR and OUTR registers communicate serially with a communication interface and in parallel with the AC.
The transmitter interface receives information from the keyboard and sends it to the INPR register.
The receiver interface collects information from the OUTR register and transmits it to the printer serially.
Design of a basic operator.
A basic computer is composed of the following hardware components.
- A memory unit containing 4,096 words, each 16 bits in length.
- Registers include AC (Accumulator), DR (Data Register), AR (Address Register), IR (Instruction Register), PC (Program Counter), TR (Temporary Register), SC (Sequence Counter), INPR (Input Register), and OUTR (Output Register).
- Flip-Flops: I, S, E, R, IEN, FGI, and FGO
- Two decoders: a 3x8 operation decoder and a 4x16 timing decoder.
- A common 16-bit bus
- Control logic Units
- The logic and adder circuits are connected to the input of the AC.
