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Precise JavaScript emulation of Intel 8080 CPU

Based on BSD-licensed work by Copyright (C) 2008 Chris Double

All flags and instructions fixed to provide perfect compatibility with original "silicon" CPU.

This emulator passes the Exerciser

Big thanks to Roman Borik ( His help lets me achieve such a perfect HW compatibility.

Used in all emulations at ASM80 online IDE


(a.k.a. The API)

  • window.CPU8080 - main object (instantiated at the start - it shall change)
  • CPU8080.init(memoryTo,memoryAt,ticker,portTo,portAt) - Initializes the whole system. All parameters are callback functions for port / memory access:
    • memoryTo(addr,value) - store byte to given address
    • memoryAt(addr) - read byte from given address
    • ticker(T) - unused. For future use
    • portTo(addr,value) - write byte to given port
    • portAt(addr) - read byte from given port
  • CPU8080.T() - returns clock ticks count from last init (or reset)
  • CPU8080.reset() - does a CPU reset
  • CPU8080.set(register, value) - sets internal register (named PC, A, B, C, D, E, H, L, F, SP) to a given value
  • CPU8080.status() - Returns a object {pc, a, b, c, d, e, h, l, f, sp} with actual state of internal registers
  • CPU8080.steps(N) - Execute instructions as real CPU, which takes "no less than N" clock ticks.


  • window.CPUD8080 - main disassembler object (instantiated at the start - it shall change)
  • CPUD8080.disasm(i,a,b) - Disassembly instruction. You have to provide 3 bytes - first one is an instruction code, second and third are parameters (they can be omitted when instruction is single byte or two bytes). It returns an array of two elements: the first is instruction mnemonics, the second is an instruction length.

You can use 8080js also as Node.js module.


8080js is slightly tested with qUnit - just a basic functionality at this moment

Use emu8080test.html for testing with a real test suite


  • Change it from self-called constructor to real class
  • Prepare exerciser as inline test


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Precise JavaScript emulation of Intel 8080 CPU




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