Mano Basic Computer Simulator

Problem

Mano's Basic Computer, from M. Morris Mano's Computer System Architecture, is the textbook machine many computer engineering students first learn processor design on: a 16-bit accumulator machine with 4096 words of memory, a small register set, and a common bus. On paper it is easy to follow one instruction. It is much harder to see how the control unit sequences micro-operations across many clock cycles, which is exactly where students get lost.

Approach

The simulator models the machine at the level the textbook teaches it, one micro-operation at a time, instead of interpreting instructions as black boxes. Each clock cycle advances the sequence counter, asserts the control signals for that timing step, and moves data across the bus between registers and memory. The result follows the datapath diagram step by step, which makes it useful for checking a hand-traced program.

Architecture

The simulator is written in Python and models the full datapath: the registers, memory, and common bus, plus micro-operation level control for the fetch, decode, and execute phases of each instruction. The full instruction set is supported: memory-reference instructions such as AND, ADD, LDA, STA, BUN, BSA, and ISZ, the register-reference instructions, and the input-output instructions.

A command-line debugger sits on top for stepwise execution and state inspection, so you can walk a program through the machine and see what each step changed.

Why cycle accuracy

An instruction-level interpreter would reach the same final register values, but it would hide the part the course is about. Modeling each timing step makes the extra cycles of indirect addressing and the order of register transfers visible, which is the difference between knowing what an instruction does and knowing how the hardware does it.

My role

I wrote the simulator and debugger myself. The source is public on GitHub.