z80js

z80js is a Javascript Z80 disassembler and program debugger.

It's highly inspired by libz80 C library by Gabriel Gambetta but apart from my complete Go port https://github.com/viert/z80 this one is done from scratch with more accurate timings, smarter code generation and designed to pass well-known z80 fuse tests (included).

All officially documented Z80 instructions http://www.zilog.com/manage_directlink.php?filepath=docs/z80/um0080&extn=.pdf are implemented and passing tests.

z80js is designed to work in browsers and being developed to become a part of http://t.z80online.net online Z80 assembler/debugger

Building

• git clone
• npm i to install dependencies
• npm run build to build dist/z80bundle.js

Using the library

z80bundle exports Z80 class which can be instantiated like let cpu = new Z80(mem, port, debug)

mem has to be a memory instance with methods read8(addr) and write8(addr, value) reading and writing data from/to memory correspondingly. An example memory class can be found in src/memory.js and is absolutely ready to go memory class used in tests.

port is an I/O device instance capable to read and write data from/to devices. Must have ioread(port) and iowrite(port, data) methods. An example class can be found in src/port.js however this one simulates a single device responding with data being passed via the high byte of a port, i.e. if you read from a port 0xFE34, it will return FE. This is basically how fuse tests are testing port instructions.

debug is a boolean to switch the debug mode on and off. In debug mode the library logs a lot of debug data during running commands.

After creating a cpu instance just run cpu.execute() - this will run a single cpu instruction located where PC register points.

cpu.disassemble(addr) disassembles an instruction by address addr. If no argument is given, the next instruction is being disassembled (i.e. addr equals cpu's PC register). For convenience disassemble method returns an object with fields dasm containing the disassembled code string and nextAddr for you to know what the address of the following instruction is.