I want to build a legacy product (Mockingboard
for the Apple IIe
). I have built one on a breadboard using vintage parts. I believe I can replace the audio chip (AY-3-8912
) with a propeller.
But, I can't seem to find an alternative to the 6522 VIA
IC.
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_43254_-1
Granted, it appears these are still made. Maybe because nothing easily replaces them?
Anyway, is there a more modern alternative? Something that is surface mount or just a smaller package?
The project I want to make would be very small quantities but the board space is minimal and these chips are ginormagantuan.
Thanks
Best Answer
I would suggest that you might be able to use an ARM to emulate the entire Mockingboard with an ARM running a very tight loop, especially if you know which features of the board software will be relying upon. It would likely be necessary to write everything in assembly language, but some ARM7-TDMI chips can run more than 64 cycles for each 6502 bus cycle. While perfect emulation of the chips in question might not be possible within those time constraints, it should be possible to come close enough to satisfy Apple II software that wants to talk to the Mockingboard.
BTW, the propeller may be a good choice for tone generation, but an ARM7-TDMI could do pretty well also. Code to emulate three voices would be: