(Updated on 6/5/2020, schematic diagram)
Finally work on the
I/O interface card has begun. I finished the circuit design and completed some parts
for a prototype. Of course first prototype will be built on a breadboard,
however I am thinking ahead about a more
permanent working prototype. I want to build it as a small daugtherboard that
will plug into a custom socket in the motherboard. The I/O chip used is
WDC65C22S. D2 is supposed to be a low voltage (<0.5 V) diode since IRQB is a
totem-pole output (unlike the classic MOS6522 with open drain output). I am
thinking a Schottky diode, but haven't decided on the type yet. Two 16-pin
ribbon sockets will be used as connectors for ports PA and PB. 20-pin single row DIP sized connector will be
a plug-in to the motherboard to connect the VIA chip to all necessary
microprocessor signals.
