Z80 CPU Emulator

Introduction

This is a Z80 CPU emulator written in C#. I have created it as a fun project. It is quite generic and possibly can be used in any project that requires a Z80 CPU emulator.

There is also my own fork of this project that adds some features specific to the ZX Spectrum, like memory contention handling. I simply wanted to keep this project as generic as possible.

Features

• Full Z80 instruction set
• Undocumented instructions (at least the most common ones)

Implementation

• The emulator is written in C# 12 and .NET 8
• Source files are kept small and clean using partial classes
  • The main class is Z80.cs
  • Instructions are implemented in a separate files based on logical groups:
    • 8BitArithmeticInstructions
    • 8BitLoadInstructions
    • 16BitArithmeticInstructions
    • 16BitLoadInstructions
    • BitSetResetTestInstructions
    • CallReturnRestartInstructions
    • ControlInstructions
    • ExchangeBlockInstructions
    • GeneralPurposeArithmeticInstructions
    • InputOutputInstructions
    • JumpInstructions
    • RotateShiftInstructions
    • UndocumentedInstructions
• There are 3 types of tests:
  • Unit tests (I have written a very basic Z80 assembly parser to help me write these)
  • Fuse tests (tests that come with the Fuse source code)
  • Zex tests (command line runner of the Z80 instruction exerciser)

Testing

The emulator has been tested using the following test suites:

• Fuse tests
• Zex tests
• My own unit tests

Usage

There are two interfaces that can be used to interact with the emulator:

• IMemory
• IBus

The IMemory interface is used to read and write memory, while the IBus interface is used to read and write I/O ports.

As a minimum you need to implement IMemory to be able to run the emulator. The IBus interface is optional.

The following is an example of a simple memory implementation:

public class Memory : IMemory
{
    private readonly byte[] _memory = new byte[65535];

    public byte Read(ushort address) => _memory[address];

    public void Write(ushort address, byte data) => _memory[address] = data;
}

Then you can create an instance of the Z80 class:

var memory = new Memory();

memory.Write(0, 0x3E); // LD A, 0x12
memory.Write(1, 0x12);

var cpu = new Z80(memory);
cpu.Run(7); // Run for 7 cycles

References

• Z80 CPU User Manual
• Z80 OpCodes Table
• The Undocumented Z80 Documented