While I was making my cart, I put a frequency counter on A12 and got about a
1Mhz for access. I now this isnt the best way to do it, but it was enough for
me to realize that there was no way my microcontroller was going to be able to
make it. Remember that some microcontrollers take multiple clock cycles per
instruction. I was running at 20MHz but, at 4 cycles per instruction I was
really at 5MHz. Thats at best 5 instructions per cart read! Not enough time
for me. I looked into CPLDs. I have always been afraid of them, but after a
little research they are a piece of cake to use. Look into Xilix XC9500
series. The design software is free and I found a tutorial at http://www.al-
williams.com/pbx84.htm. I even ended up buying the al williams development
board and programmer (which is incredibly cheap compared to anything else I
could find). Their programmer works with the Xilix software. If I can figure
it out, anyone can.
Tip: When prototyping, keep those address and data line SHORT coming off the
VCS!!!!! And try to stay away from breadboards.
Good luck!
Vern
> My last concern is timing. How long do I have to get valid data on
> the bus once the 2600 has set up the address lines?
> The FAQ lists the bus speed as 1.19 MHz. Does that mean I have
> less than 840 nS to get the data lines valid?
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