Hi,
I fooled around with this a bit yesterday. I've got a software solution for generating three tones but there is (and won't be) any noise, mixer, envelope, shape and whatever else the AY-3-8910 can do - just three tone generators. I have no idea if it'll work in practice or how good it'll "sound" but scope and frequency counter shows correct values for, at this point, three octaves.

With 3 channels it will NOT work at 4MHz, it MIGHT just work at 8MHz but there won't be much left do anything else. I'm currently running it on a 18F25K20 @64MHz so I need to breadboard something with a less capable chip and see what gives. Obviously the lower the maximum output frequency needs to be the more can be achieved with a low clock frequency so I'll ask again: What's the maximum output frequency you NEED?

Is the 12F683 the desried target chip and will you able to run it with external clock (to get 16MHz or 20MHz)? As it's written it relies on the prescense of a TMR2 module and uses interrupts at the ASM level, though the actual ISR is written in PBP with manual system register save/restore.

Are you aiming to do other things as well with this same chip?

It's not ready for public viewing yet, I'll post it when it is (or not if the answers to the above questions shows it's a dead end....)

/Henrik.