Whether you want to build your own C74-6502, or just learn more about its inner workings, this is the place to dig deeper. This section provides detailed explanations of the circuitry in each PCB of the project, as well as a collection of useful downloads and all project files.

You may also want to have a look at the Original Build Thread, where design details were discussed live as the project developed.

(This page is a work in progress. Information will be posted as it becomes available. Please send us a note if you would like to be notified when technical information is posted.)


  • Block Diagram
  • Card A – Registers, 6510 port, clock and pinout
  • Card B – ALU, CU, Undocumented Opcodes (UFO)
  • Card C – K24 Address Bus Extension (ADX), SPI interface
  • Card D – C74-SBC Single-Board-Computer Test Environment
  • Card S – C74 Host Socket Adaptor
  • Microcode
  • Optimizations

Useful downloads

  • C74-6502 Draft Datasheet (.pdf)
  • Critical Path Analysis (.pdf)
  • Control Logic Decoder Values (.pdf)
  • Microcode Pipeline Notes (.pdf)
  • 6502 Undocumented Opcode Notes (.pdf)
  • 65816 Opcode Notes (.pdf)
  • Clock Loads Notes (.pdf)
  • Microcode Source (.pdf) / (.xlsx)
  • Logisim Model (.circ)

Project Files

  • Schematics (Eagle CAD .sch)
  • PCB layout (Eagle CAD .brd)
  • PCB Assembly Guide (showing part numbers .pdf)
  • PCB Boardview (showing silkscreen labels .pdf)
  • PCB Gerber files in ???? Format (.zip)
  • PCB BOM files (.xlsx)
  • Microcode ROM assembler source files (.65S)
  • Microcode ROM binary files (.65b)
  • C74-SBC C74-Minimon Assembler Source
  • C74-SBC ROM binary files

[Download project files (.zip)]