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I am trying to rehab a machine that was built using a 6522 and 2-6821s (and a number of secondary chips) for its control functions by replacing them with a SuperPro and 2 Prostarts(avoids having to deal with interrupts). When I trace the digital outs from the original chips, they all seem to connect to inverting buffers. Was there something about these chips that made using inverting buffers necessary?

Thanks

Hard for me to answer this as I have no data to go on. Maybe there was a reason for drive capabilities of those now 40 year old parts. I was around then and using 6502 in Apple, never saw 6522.

You would have to look at the spec sheets for those parts and how they are used in the circuit.