Posted By
dmantione
on 2022-09-05
18:29:28
|  Re: External User Port for the C16: Let's make it!
Hi guys,
First post here on this forum. I am certainly willing to share my 6529 schematics, I'll get back to this quickly. It's quite simple: A 74x402 that generates the control signals for a 74x654. If you are already using a GAL, you can consider to use the GAL to generate the control signals and remove the 74x02.
About the cassette sense problem, main issue I see is that it activates both for reads and writes to $FD1X, if it would have been read-only you could have decided to use the existing circuit for reads to D2, but any write than the 74x125 on the C16 mainboard will cause a bus conflict.
You could consider to solve the cassette sense problem with a custom PLA that doesn't decode $FD1X. It'll cause some cassette compatibiliy issues but then you can make the user port cartridge fully compatible. It's a pity that none of the TED PLA lines are connected to the cartridge port, otherwise it would have been far easier to create an elegant solution.
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