J-PCU, FPGA 6510/8500

FPGA 6510/8500 - J-CPU

  • FPGA based replacement for MOS 6510 CPU
  • Project started in 2020 by designing PCB. No PCB was populated until summer 2022, when the project continued.
  • Project goal is to make 100% compatible FPGA replacement for MOS 6510, that is physically same size as original
  • One goal is to learn more about FPGA designing, so all the code is completely self written
  • October 2022 status:

  • About 80% complete. Already usable, with some issues with some games and demos
  • PCB needs some modifications
  • All standard instructions implemented
  • Cycle count not correct with all instructions
  • Decimal mode not implemented
  • Only some illegal instructions implemented so far
  • IRQ interrupts ok, NMI not implemented yet
  • RDY/AEC logic done and working. HALT timing needs to be checked
  • Bus timing needs to be checked and adjusted.
  • January 2023 status:

  • Decimal mode implemented
  • All except some unstable illegal instructions implemented
  • NMI implemented
  • Still not correct cycle count with all instructions
  • New PCB:
  • February 2023 status:

  • Very many bugs fixed
  • Cycle count is now correct with all instructions, except 2 unimplemented illegal & unstable instructions
  • Even many demanding PAL-demos work now
  • Even though mostly works correctly, there is some problems with IRQ, NMI & RDY signal handling, especially when they are overlapping
  • Some problems with decimal mode, especially with flags when decimal mode is active
  • April 2023 status:

  • Once again many bugs fixed
  • Cycle exact with every instruction now.
  • All illegal, including the "unstable" instructions implemented. "unstable" functionality needs some checking and possibly fixes
  • Decimal mode works correctly with all instructions, including illegal instructions
  • Still some problems with interrupts & rdy
  • Small problems with phi2 clock signal output
  • New PCB drawn & ordered, hopefully fixes some small stability issues and phi2 output

  • Check out also: J-CIA / J-VIC / VIDS

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    Finland 2020-2023 Jani Laatikainen