AY-3-8910/12/13 "module"

[factus10]

I've been thinking about building an AY-3-8910 module for a year or so and finally started laying out a schematic over the past few weeks. I'm still deciding how many knobs, etc, to put on it but it'll also have a PIC that'll receive MIDI for it (and drive the display, A/D the knobs, etc). Eventually I'll probably also add MIDI send (to d/l sysex).

Am I the only one crazy enough to want such a thing?

[DrJustice]

[v-un-v]

To be honest, I always thought that the AY chip was just a watered-down version of the SN76477 chip. A friend of mine had a BBC micro which had an AY in it, and I thought it sounded awful.

You may very well be mad, but otoh..........

[DrJustice]

For what ist's worth, natively the BBC had an SN76489 which had three counter based squarewave oscillators and a noise source, each with an amplitude control. The AY-3-8910, which was similar, but a bit more advanced, was used in a lot of the early home computers like Atari and ZX Spectrum. The SN76477 was more or less a simple analog synth voice.

Anyway, they're all the stuff of good memories

DJ
--

[factus10]

The AY had some advantages (and disadvantages) in relation to its peers. It's SID-like not as powerful but it's been a while since I've programmed the SID. And it has slightly better envelope control than the 76489.

It was used in MSX computers, Atari ST (and later), the Orchestra 90 cart for the Radio Shack Color Computer, Spectrum, and the Mockingboard (a synth for the Apple that used 3 AY chips). Apparently it was wildly popular in arcade games.

Thanks for turning me on to the 76489. Another potential project

[v-un-v]

[State Machine]

Sounds like a project that would be worth the time simply due to the fact that you are keeping "alive" some of those god old chips from the 80's. Sure you could not only use that PIC for the MIDI control, BUT, could also do the sound generation better than the AY chip. That would take the fun out of using that vintage chip you have always wanted to play with.

I believe you can play a trick with the AY-89xx chips by setting an oscillator with a zero frequency value and then command a series of VOLUME messages to have it act as a low resolution DAC. Then you can do simple speech and other sampled sound FX

I have about 20 of these chips in my stash !!!

[CJ Miller]

I agree that a PIC or other decent MCU is overkill for such a project, since such chips could just as easily replace the AY itself anyway. But they are still cool chips, especially if you love olde schoole square wave chip tunes. For instance I have random 8085 and 8088 processors in my junk box so it could be a fun excuse to put something together. Maybe ADCs for analog-controlled chip tunes would be fun.

I found 12 AY-3-8910 and 1 8912 for $5.50 last week, and figured they were worth the minimal cost to play with. I agree that the SID is way more robust, if anybody has 12 of *those* they want to sell me for $5.50, let me know! ;]P

[State Machine]

[Tony Deff]

Wow! Someone else is still using the AY-3-8910.

I hung onto a couple of these out of sentimentality, but in truth they are fatally flawed, musically.

Because the clock input (which is already severely limited in frequency) is divided by a prescalar of 16, the remaining programmable divisor to obtain the required note is too small to get a pitch precise enough for equal temperament (except perhaps for bass notes).

To get around this problem, I used the Just Scale in a design published in ETI in 1989 for a polyphonic doorbell (!)
It belted-out an impressive version of Star Wars, complete with phasing noise effect.

The circuit used a Z80 and PROM (but no RAM) and used the register codes of the 8910 chip to implement a compact (1K) "interpreter".
To use this interpreter, the user entered simple single-byte or dual-byte codes which would set-up the required registers or implement software routines.
A single byte would, for example, set the required divisor for middle-C in any of the 3 divisors, whilst another single byte would set-up the registers to implement an attack and then delay for the required note-time. Sub-routines without RAM are possible by exploiting the Z80's rich register set, and this allowed whole chunks of music to be repeated in just a few bytes of coding.

I kept the 8910s wondering if the crude D-to-A converters would be useful to bias a wide-ranging phase-locked-loop quickly into the required frequency range.
Pity I got rid of all the spare PCBs a couple of years ago!

[blue hell]

Tone-Deaf,

never would have expected to hear about a new (for me) z80 trick after, what is it ... 20 years or so

[State Machine]

[State Machine]

[Tony Deff]

[State Machine]

[State Machine]

[factus10]

I recall the tuning issue when I first contemplated this a number of years back. In one of my notebooks, I have a table of the various note/register values for whatever osc I had chosen.

I'll have to go take another look at the Orchestra-90 cart for the Radio Shack Color Computer to see what clock they used. As I recall, the shortened version of William Tell built into it didn't sound that off

[State Machine]

[Tony Deff]

When choosing the clock frequency and the divisor, bear in mind the intervals between the notes.

For any single note, you can optimize either as you wish; if the 8910 could be forced to gallop at 2.4576 MegaSquirtz, then a divisor of 311 will give you an excellent B = 7902.

If you want a series of notes in a reasonable semblance of the equal-temperament scale, then one of the well-known divisor sets must be chosen, otherwise all sorts of scaling errors and/or locked intervals can occur.

For example, you have found a good B = 987.766 with a register value of 127. The register value of 142 gives you A = 883.425, but that means the step from A-B is 6.7 cents too small.

Sorry to be a kill-joy, but I think we should keep our fond memories and bid the 8910 farewell.

The 8253 has 3×16-bit dividers that can operate at 8 MegaSquirtz

The ML2867 can operate up to 27MHz. and has a 64-poly synth with General Midi set. Will one day we be looking-back senimentally at this?

[State Machine]

[factus10]

Heh... high fidelity isn't exactly my goal in this

[State Machine]

[Tony Deff]

Anyone want to "play" with a Programmable Sound Generator?

I was too sentimental, and have found that I retained several glass-fibre single-sided PCBs for my Programmable Doorbell (Polybel) project (vintage 1989 — gosh! Tempus Fugit)

You may have to chop and change to get what you want.

It interfaces an AY-3-8910 to a Z80 and a 2K EPROM/EEPROM (2817)
There is no RAM involved — clever interfacing (even if I do say so myself) uses the Z80's WRITE commands (normally used in a CALL Subroutine command) to set-up the PSG's control-lines via an LS139.

An efficient "interpreter" was written that takes up 256 bytes of the EEPROM: the other 7 "pages" are taken up by "tuneware", selectable by a rotary switch. Of course, you can do your own thing here, but this saves an awful lot of code-writing!

Setting the registers to select one of 32 notes of the Just Scale takes just 1 byte. Another single byte sets one of 16 tempo-related timing delays.
Two output port bits are used to control a crude filter, and two are free for your use, all set by a single byte. The interpreter allows for "recalls" (a repeat of a passage) and for "escaping" into your own machine-code.


This board takes-in a 6V battery supply and passes it through a "bistable regulator" comprising an LM10 op-amp with reference (that are hard to come by these days — I may have a couple left). (I also have several NEC CMOS z80s going spare)
Regulated +5V is produced when a pushbutton is pressed, and is turned-off by a HALT command from a Z80.

There is also a small patch-board area.

Last, but not least, you can program the thing from a PC printer port.
The catch is, you have to have the software already loaded into EEPROM, and I no longer have the means to do this!

The cost? — Basically free, but if you want photocopies of all the documentation, I cannot afford world-wide postage. In the UK, send Stamped Addresses Envelope; to Europe, offer an exchange or plead poverty, in more exotic climes, write an open invitation to laze by your swimming pool!

[new voodoo]

I am DEFINATELy interested.
Ive got some 8910/12s and Ive got maybe 20, so Id LOVE to figure out a relatively cheap way to make about 18 devices to dessiminate to some friends and the alternatives that i can find seem to be PICs and Arduinos to run it and that does seem counterproductive.
I have the vague sort of hope that id like to make it a bass synth primarily so..not too heavily concerned with perfection at higher frequencies..just with making it work and getting them to play.

[new voodoo]

im thinking ill add a little board off to the side with perhaps a 2399 simple delay circ, a 308 rat-type distortion with perhaps 3-4 diode clipping choices and a simple 7-band eq from some eq chips I have laying about and then running it all thru a matsuhita-type tube overdrive using a 12au7 or 9au7 vacuum tube thickening up the sound so I can run the whole sound section from a 9v..so hopefully making it really killer.

just an idea. we'll see how it progresses. got about 11 other projects currently on various front burners