Microprogrammed Control System

Overview

Microprogrammed Control System for digital computers, offering an elegant alternative to hardwired control units.

Key Components

1. Microoperations

Detailed low-level instructions (micro-ops) for CPU to implement complex machine instructions.

2. Micro Instruction

Symbolic microprogram translated into binary, with fields like label, microoperations, CD, BR, and AD.

3. Control Unit Organization

Configured using a block diagram, assuming a ROM for permanent storage of control information.

4. Address Sequencing

Steps during a computer instruction execution:

• Step-1: Load initial address.
• Step-2: Determine operand's effective address.
• Step-3: Generate microoperations based on instruction code.
• Step-4: Execute instruction and return to the fetch routine.

5. Mapping of an Instruction

6. Computer Hardware

7. Instruction Format

1-bit indirect addressing, 4-bit opcode, and 11-bit address field.

Examples:

• ADD: Adds operand to AC.
• BRANCH: Branches if AC is negative.
• STORE: Transfers AC content to memory.
• EXCHANGE: Swaps data between AC and memory.

8. Micro-instruction Format

20 bits with F1, F2, F3, CD, BR, and AD fields.

9. Subroutines

• FETCH AND DECODE: AR <- PC, DR <- M[AR], PC++, Read, Increment PC, Read DR, Transfer to AR and CAR.
• INDIRECT: Read, Transfer to DR and return.
• ADD: Read EA to DR, AC += DR, NOP, Call Indirect, Read, Jump to Fetch.
• STORE: M[EA] <- AC, NOP, Call Indirect, AC to DR, Write, Jump to Fetch.
• EXCHANGE: M[EA] <-> AC, NOP, Call Indirect, Read, Transfer to DR and AC, Write, Jump to Fetch.
• BRANCH: If (AC < 0), PC <- EA, NOP, Jump to Fetch.

Using Logisim

Logisim is employed to simulate and visualize the functionality of the Basic Computer. It provides an intuitive toolbar interface and supports the design of digital logic circuits.

Instructions for Simulation

→ Open Logisim.

→ Load the provided circuit file (MAIN CIRCUIT.circ).

→ Simulate the circuit to observe the Basic Computer's behavior.

Here is a view of Arithematic and Logic Unit of My Microprogrammed Control Computer

Here is a view of Control Unit of My Microprogrammed Control Computer

Here is a view of My Microprogrammed Control Computer

Contributors

• Shubham Dwivedi
• Shashvat Tiwari
• Vaibhav Mishra

Acknowledgments

• Thanks to Dr. Alok Kumar (HOD, IT Department, UIET Kanpur) for helping through out working on this project.