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.


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3 comments:

  1. Corneleous Worthington26 May 2016 at 14:19

    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: www.putnamelectronics.com

    Thanks for posting your projects! Fascinating stuff!
    Jason

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  2. Vossi27 May 2016 at 07:23

    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.

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  3. Kakemoms8 June 2016 at 06:11

    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.

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