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Re: [N8VEM-S100:5099] 6502 CPU board questions

Hi Gary,
I'm glad you have your board working now. Goodness knows what the problem with the WDC W65C02 is though! It must be something very subtle.

On Sun, Aug 31, 2014 at 5:56 AM, <geka...@gmail.com> wrote:
Ian -

I wish you were a bit closer, as I certainly owe you a beer.

There is something about the W65C02S beyond just pins 1, 5 and 36 that is causing a problem with the S-100 6502 board.  Pin 1 (Vector Pull) and Pin 5 (Memory Lock) aren't connected to anything (I bent them out of the socket to be sure) and pin 36 (Bus Enable) is tied to VDD (Pin 8) already.  Interesting the board is able to access I/O ports fine - but can't read/write properly to RAM that is over the S-100 bus.

In any case, a Rockwell R65C02P4E fixed the problem (after 2 weeks of hair pulling) and seems rock stable at 4mhz.

If anyone else has had success with the W65C02S I'd be interested in hearing - otherwise it might be worth a mention on John's site so others can avoid this gotcha'.

Many thanks to John and Ian for the debugging help!

- Gary

On Friday, August 29, 2014 11:15:09 AM UTC-4, Ian May wrote:
Hi Gary,
Have you made the changes for the WDC W65C02S6TPG-14 listed here http://www.westerndesigncenter.com/wdc/AN-002_W65C02S_Replacements.cfm ? If you haven't I would suspect that your address and data buses are going tri-state due to a floating BE pin. This was also discussed in the other N8VEM group here https://groups.google.com/forum/#!topic/n8vem/JL1ubJlH4HY .

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