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W65C265S Single-Board Computer

Updated: 12 minutes ago

It has been a few years since I have worked with the 6502 and 65816 processors. Most recently, my focus has been learning about FPGAs and developing my own FPGA PCB. Along the way, I designed some retro 286 and 386 systems, dabbled with a variety of microcontrollers, and learned more about PCB design. I thought it might be fun to build a single-board computer (SBC) based on the W65C265S microcontroller from The Western Design Center (WDC).


This post will be updated as I work through the design and build. I will be learning as I go through this, and I expect to learn regularly from my mistakes. :) As with all of my projects, I will also learn from feedback and suggestions you have. Also, I expect to iterate through designs, incrementally improving the SBC.


Fortunately, WDC has a reference design for a W65C265S SBC. This, along with previous work I have done on my 6502 and 65816 systems, should prove to be helpful. (Looking at the datasheet for the W65C265S, I have much to learn about this microcontroller.) That then leads me to think about my general requirements for this project.


General Requirements / Design Targets

As I work through research and design activities in the coming months, the following list will evolve.


  1. W65C265S8QG-8 (QFP 100).

  2. Four-layer PCB, designed with EasyEDA Pro, and manufactured by JLCPCB.

  3. Selectable clock, including single-step, full-speed 8 MHz, and a few options in between.

  4. Flash ROM (onboard programmable?).

  5. Static RAM.

  6. Power and reset switches, debug LEDs.

  7. Connection for offboard custom debugger.

  8. Connection(s) for expansion PCBs, using XBus265 or an extension of it.

  9. Leverage the WDCTools suite (assember, linker).

  10. USB serial terminal and/or RS232 terminal.

  11. 1602 LCD, or something similar.

  12. Keyboard support (PS/2 mode).

  13. Simple audio output (2-tones).

  14. Stretch goals:

    1. USB programming interface.

    2. Simple VGA output.

    3. SPI support for an OLED display.

    4. Programmable sound generator IC, such as the YM2149.


What am I missing? Suggestions?


Next steps:

  1. High-level block diagram.

  2. Datasheet review.

  3. Schematic work.

  4. PCB work.

  5. Iterate






[December 4, 2025] PCBs and parts have been ordered. I went with the slow shipping option from JLCPCB. The total PCB cost for five PCBs, plus shipping, was under $20 USD. The rest of the parts (enough to build a few boards) was about $200. Tariffs... ouch! It will probably be a month before I have everything in hand. In the meantime, I can work with the W65C265SXB board that should arrive yet this week.



More to come!


Project Files

I will post project files here, starting with the current schematic. As I get to coding, I will add a project to my GitHub and link here.




Resources


Additional Info



Interesting Tidbits

Below are miscellaneous things that are catching my attention as I work on this project.


  • The W65C265S has the full 24-bit address and data bus available as opposed to the W65C816S having the high order 16-23 address pin multiplexed with the data bus.

  • Page 63 of the W65C265S datasheet (dated March 18, 2024) appears to have a typo in the schematic. The upper crystal is correctly labeled XTAL1, but the lower crystal is incorrectly labeled XTAL1. The lower crystal should be XTAL2.

  • Page 5 of the 65xxcelr8r Board Datasheet (dated October 31, 2014) shows the USB connector as J5, but the PCB silkscreen and schematic show it as J6.





 
 
 

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