Sorry that I haven't provided more information on the design. Mainly because I'm still in the planning stages. I *HAVE* actually built a similar design twice on a breadboard. That design had no 3v3 parts. So it was just a matter of tapping into the Apple IIe +5v power supply through the slot connector.

My new design will roughly consist of:

Two 65C22's, one Propeller micro-controller and an op-amp (or two).

The only part that must be powered at 3v3 is the Propeller.

Each of the 65C22's will be connected to the Propeller. Each 65C22 will have Port A (all 8 pins) tied to a pin on the Propeller. Total 16 pins.

Each 65C22 will have 3 pins of Port B tied to the Propeller. Total 6 pins.

The Propeller will have two pins of audio (PWM) going into an op-amp (maybe two...not sure yet).

A7 will go to the enable pin of one 65C22 and !A7 (through an inverter) will go to the enable pin of the other 65C22 and the Propeller. That would normally be a 5V signal since it's coming from the A7/slot. So I will need a level shifter there.

Finally, the O1BUFF from the slot will feed into the Propeller as a clock source (also 5V).

Keep in mind, this is a back-of-the-napkin design. I haven't had time to finalize anything yet.




This topic has been discussed to the "n'th degree" on the Parallax forums. Many different expert opinions. From what I can tell, unless I *really* know what I'm doing and building (which I don't...) then the safest bet is to use level converters.

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Cat; the other white meat.

Alright, this part is fairly clear. I know A7 is an output from the 6502, and I know the 6522's "enable pin" is an input.

This part still lacks detail, I'm afraid. Words like "connected" and "tied" don't reveal which direction the signal travels. The 6522 is capable of operating the Port A and Port B lines as inputs or outputs -- and indeed some applications switch modes on the fly, rendering one or more port pins bi-directional. I expect the Propeller pins are equally flexible -- input, output or switching between input & output. For each of 16 + 6 lines, please tell us which direction(s) the signal travels. Is it a signal output by 6522 which gets input by the Propeller, is it vice versa, or does the signal direction change (bi-directional)?

Even with level converters you still need to know the signal direction. An exception would be that Sparkfun gizmo, which no doubt will work with some stuff but IMO it's a question mark for your project, at least until we learn more about what you're up to.

I like the idea of a sound synth, BTW. Seems like a cool thing to play around with.

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

I'm as confused as Jeff.

Is this based on an existing design and does it have to be compatible, and if so, how? That'll answer many of the questions, especially if there is a schematic or technical documentation for it.


Edit, much later:

Ok, I have read a few of the recent topics and have a better idea what it is you want to do - emulating one or two AY-3-8910 sound generators on a Propeller, and I'm assuming you'd want to be software compatible. I'm also assuming that using a VIA inbetween is something that is already done, and not a new invention that would require patching existing programs.

I don't see why you would have to duplicate all the hardware exactly, though - as long as it looks the same to a programmer it should be fine, right? So here is what I was thinking:

Assuming you don't have to read from the emulated AY chip, you'd have to level-translate eight data lines plus at least one handshake line. Port A on the VIA has a handshaking mode that looks useful; if you use the "pulse" mode, the Propeller would get a notification every time something is written to port A. This would be an 8-bit unidirectional data path, using nine signals.

But you need to distinguish between address writes and data writes. I'm assuming that's one of the functions that you would have on port B, so that's one more signal.

Multiple emulated chips? Well, the Wikipedia article on the AY-3-8910 mentions that the address write has to have the upper four bits set to "0000", except for customized chips. With customized chips, you can "control more than one AY chip on the same bus (e.g. Mockingboard sound card)" - so does that mean that software already supports it, no more control signals are needed, and we only have to teach the Propeller how to distinguish between bit patterns? If that's the case, we're done.

Otherwise, I guess we need one more signal - port B again, or using an address decoding trick make one VIA look like two and grab a signal there.

So it looks to me like ten or eleven unidirectional signals. Oh, and the clock.

Let me know what I missed.