Monday, April 22, 2019

I/O interface card for MKHBC-8-Rx computer


(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.





MK 4/23/2019

Reset And Panic Buttons, Buttons Debouncing

Reset And Panic Buttons, Buttons Debouncing The monitor program in my home brew computer has a nice debug feature. The NMI (Non-Maskab...