Sunday, 12 April 2015

Problems with WDC W65c02

I made my new PLCC-adapter with 4 jumpers switchable between Rockwell/CMD and WDC.
After I got four W65c02-10 I tested them all on the breadboard.

Everytime I had stability issues with my LC64 on the breadboard I changed the WDC CPU to the Rockwell - and all is OK!
  • The WDC is not TTL/NMOS-compatible
  • W65c02 has a more critical timing - it's for 10 MHz.
Also I tryed the BE-input to disable the outputs with the AVR. Than the AVR read the screen-memory from the RAM and printed it to the TFT.

But the WDC runs not stable in the system and I decided to use the good old Rockwell and adress-buffers with OE. The Rockwell 4MHz CPU runs without any problems @ 5 MHz - that's enough for me and the fast 90ns-eprom.


  1. That is quite interesting about the WDC 65C02 not being stable at low speed. I'm building a 6502 computer now, and using the PDIP version of WDC65C02, and have not experienced any issues with crashing at all. I'm currently running it at 1MHz.. I wonder if you got a bad one?

    Neat project by the way- may just have to try to get a homebrew C64 working after seeing your site! I've got a link to my homebrew computer projects (on youtube) on my website:

    Thanks for posting your projects! Fascinating stuff!

  2. Hi, thanks for the comment.
    I have four WDC 65c02 cpu's and all have the same stability problems in my project.
    All my CMD and Rockwell 65c02's run perfectly.

  3. How is the design doing at 10MHz? You have to be considerate on logic delays if you use discrete components at higher speeds. E.g. the timing variations may affect a 10+ MHz component while its fine for a slower one.