When I closely examined them on the photo I decided that they are indeed counterfeit products.
I'm disappointed that these chips are not what they appear to be. But at least you got something functional (apparently, so far). Of course the red flags are up. No quality control assurance on
these babies!
By the way, where can I get information about these 8mhz parts?
I haven't checked what's in the 6502.org document archive but here's an old GTE datasheet for 8 MHz '816 and '802.
Not sure what to say about your 12 MHz test. There are several things that could cause a failure at high frequency. Can you post a photo of the test rig, especially showing the bypass caps and the counter etc used to generate the clock? What type of IC are you using for the counter?
A quick hack on the breadboard. I use a 74HC4040 12 bit counter IC. 220nf caps are there for all the supply pins to the parts. Logic analyzer's cables disrupt the view. I removed the reset part and feeded counter's most significant output to the reset pin so cpu would reset every 2^11 cycles.
Nice trick with the Reset! But, from what I can see, connections to the bypass caps have a lot of room for improvement. Admittedly it's a contradiction that you would be using a breadboard to create a circuit whose maximum clock speed you wish to determine. But if you MUST go that route then I suggest the bypass cap for the CPU be attached to the chip itself -- soldered on top, straddling the 40-pin package.
Sorry for the delayed response—it's been a long and busy day.
I've been swapping E-mail with David Cramer at WDC, who in turn, has been swapping E-mail with Bill Mensch. They have never heard of Winbond making discrete devices—and I would think they'd know. I have not pulled any of this out of my hat.
Thanks for the clarification. Busy day and delayed response for me, too! It seems to me WDC themselves should already be on record with a first-person statement of who the alternative sources are, but it's not your fault that isn't the case. What's the accepted practice in the industry? It seems a sad state of affairs when a fake Winbond chip and a legit GTE chip could
both get tarnished with suspicion of being counterfeit.
[Edit: maybe I'm expecting too much. For every alternative source agreement there was probably a press release at the time. But now the info isn't easily accessed.]
-- Jeff
