My new 65C02-based retro-computer: OpenX65

I am starting a new hobby project called X65: I intend to create an open-source computer based on the “vintage” 6502 processor, which is still in production as the W65C02. The original 6502 was used in many home personal computers of the ’80s: Commodore, Atari, Apple II and so on. My computer will be called OpenX65.

Features as planned:

  • use W65C02 and (optionally) W65C816 (the 16-bit version) CPU

  • software compatibility with the Commander X16: a modern retro computer, developped by the 8-bit Guy

  • use only parts that are in production and readily available from normal distributors such as Mouser, Farnell etc.

  • no cheating by using a hidden powerful ARM processor that does some heavy lifting

  • open-source design as much as possible

  • low-cost as much as possible

  • DIY and hobby-builders friendly

The current architecture:

  • two-PCB construction: Motherboard (mo-bo) and Video-Audio board (va-bo), each board will be 100x100mm and 2-layers. This has several advantages:

    • the PCBs can be placed inside Eurocard housings

    • 100x100mm / 2-layers is cheaply manufactured by many PCB vendors

The motherboard (mo-bo) PCB will have:

  • CPU: W65C02 in the QFP-44 package

  • Memory: 2MB asynchronous SRAM

  • Lattice FPGA iCE40HX4K (TQFP-144) to handle address decoding, glue logic, PS/2 interfaces. The FPGA design will be called “NORA” = NORth Adapter, because it works as traditional north bridge in a PC. This FPGA has a fully open-source toolchain developed by the icestorm project.

  • VIA chip W65C22 (which I intend later to integrate inside of the FPGA)

  • two ports for SNES controllers, connected to VIA

  • two PS/2 ports for keyboard and mouse, handled by NORA / note: this will be more difficult than necessary to implement, if we want the Commander X16 compatibility, since they have an “arduino” for PS/2 :-(

  • RTC chip with backup battery

  • integrated debug support in the form of FTDI USB / UART+SPI chip

  • power input: 5V via USB-C port

The video-audio (va-bo) PCB will have:

  • video interface from the Commander X16, which is Lattice FPGA iCE40UP5K called “VERA” (Video Embedded Retro Adapter)

  • VGA, S-Video and composite video output ports as in the VERA design.

  • SD-card slot handled by VERA

  • audio interface - currently open… the Commander X16 uses old Yamaha synthesizer YM2151, which is 20 years out of production. Since we want to be software-compatible, I think this needs be implemented in an FPGA - either add to VERA, or additional one on the VA-Bo.

  • 10/100Mbps Ethernet port RJ45 realized by Wiznet W6100.

Overall block diagram

Current project state at E03/2023:

  • Motherboard schematic and PCB rev01 is done; waiting for the first PCB from a fab, then I will do component assembly, and test

  • Video/Audio board is not designed.

OpenX65 motherboard (mo-bo) rev01 front view