Welp, 2 weeks later and it no longer works. The only change is in software: the UART is now interrupt driven.
The keyboard is controlled by a 6522 VIA. It generates an interrupt on a timer 60 times a second. Then the irq handler scans the keyboard through VIA port A.
The VIA seems to no longer be functioning. Interrupts aren’t firing. All registers return $C0, regardless of what I write to them.
Did the chip fail, or have I done something dumb?
Microsoft BASIC for 6502 Microprocessor - Version 1.1 , complete source code for Microsoft BASIC Version 1.1 for the 6502 microprocessor, originally developed and copyrighted by Microsoft in 1976-1978.
https://github.com/microsoft/BASIC-M6502/blob/main/m6502.asm
#asm #sourcecode #git #basic #history #it #assemblercode #m6502
Ok. I’m one baby step closer to a “keyboard driver”. I have validated that interrupts work on my system.
I configured a timer in the 6522 VIA to interrupt the processor 60 times/second. My interrupt handler just increments a 32-bit int and returns.
It works! I’m able to read the “u32” value and watch it change over time.
Now on to actual functionality! #m6502 #retrocomputing
I wrote a basic keyboard scanning routine for my #m6502 computer today. You hold a key down, run the routine, and then check a memory location for the scan code.
Next, I need to write an interrupt handler to do this scanning automatically.
Ted C. Howard
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