AY-3-891x Sound Chips: Pin Assignment Differences?

[jaybird3rd]

In a post in another thread, I mentioned the Intellivision Computer Adaptor that I repaired earlier this year, and it reminded me of a question that I've had about it:

 

We all know that the Computer Adaptor adds an extra 2K of RAM to the Intellivision console, along with an extra sound chip (the same one used in the console) for extra voices and controller inputs. But, it turns out that this sound chip isn't exactly the same as the one used in the console: the chip in all of my consoles is the AY-3-8914, while the one in the Computer Adaptor is the AY-3-8917.

 

I'm having a problem with the controller ports in my Computer Adaptor which makes me think that this chip needs to be replaced (I don't think the problem is related to the repairs I did; it appeared some time later). I socketed the 8917 chip and have tried replacing it with a few known-good 8914 chips, but the sound/controllers don't work at all with an 8914 installed. I've also tried the 8917 in my consoles instead of the 8914, with the same results. This leads me to believe that the two chips are not entirely pin-compatible. I've collected information and data sheets on the AY-3-891x series in an attempt to confirm this, but I haven't been able to find much information that is specific to the 8917. Does anyone here happen to know what is different between these two chips? Is replacing an 8917 with an 8914 simply a matter of rearranging some of the pins, or are there other differences that make this impossible?

 

Thanks in advance!

 

(NOTE: I originally posted this in the Intellivision/Aquarius forum, but since this is a more technical question than most of the others in that forum, I thought it would be useful to cross-post it here as well.)

[jaybird3rd]

It seems that the pinouts are, in fact, different for each of the chips in the AY-3-891x family. I'm having trouble finding a datasheet or pinout diagram that is specific to the 8917 (I've got several for the other variations). So if you know of one, or if you happen to have a spare 8917 to sell, let me know. Thanks!

[intvnut]

It seems that the pinouts are, in fact, different for each of the chips in the AY-3-891x family. I'm having trouble finding a datasheet or pinout diagram that is specific to the 8917 (I've got several for the other variations). So if you know of one, or if you happen to have a spare 8917 to sell, let me know. Thanks!

 

I just took my ECS apart in an attempt to see what might be different about the pinout, and I must admit I'm stumped. The AY-3-8914 pinout appears to differ from an AY-3-8910 only slightly. Pin 26 is marked as "TEST2" on the AY-3-8910, but is an active-low enable input on the AY-3-8914. Likewise, pins 24 and 25 are enable inputs for the AY-3-8910 and unconnected on the AY-3-8914.

 

I don't know why the AY-3-8917 would need a different pinout than the AY-3-8914. The only thing I can think of is that they needed to do something different with the I/O drivers to support the ECS keyboard or something. (There's a nice array of resistors between the PSG and the controller ports, I'm sure you've noticed.)

 

All the pins I could easily verify (A, B, C analog outputs, the A/B I/O ports, etc.) seem to match what I'd expect from the AY-3-8914 pinout, looking at the AY-3-8917 on my ECS board.

[jaybird3rd]

I just took my ECS apart in an attempt to see what might be different about the pinout, and I must admit I'm stumped. The AY-3-8914 pinout appears to differ from an AY-3-8910 only slightly. Pin 26 is marked as "TEST2" on the AY-3-8910, but is an active-low enable input on the AY-3-8914. Likewise, pins 24 and 25 are enable inputs for the AY-3-8910 and unconnected on the AY-3-8914.

 

I don't know why the AY-3-8917 would need a different pinout than the AY-3-8914. The only thing I can think of is that they needed to do something different with the I/O drivers to support the ECS keyboard or something. (There's a nice array of resistors between the PSG and the controller ports, I'm sure you've noticed.)

 

All the pins I could easily verify (A, B, C analog outputs, the A/B I/O ports, etc.) seem to match what I'd expect from the AY-3-8914 pinout, looking at the AY-3-8917 on my ECS board.

Thanks for looking into this. The 8914 and 8917 looked the same to me, too, which is why I was surprised that I couldn't substitute one for the other. Another member pointed out that some models have different memory maps for the registers, so perhaps this accounts for the incompatibility. I did indeed notice those resistors; in fact, on some Intellivision II consoles, I've seen a similar array of resistors added to the 8914's controller port input pins. My first guess in troubleshooting my Computer Adaptor was to test these resistors with my ohmmeter, and they all checked out (1.5K, I think they are).

 

Perhaps I should describe the problem I'm seeing in more detail. In ECS BASIC or the music player, some keys on the keyboard work normally, some do not work at all, and some are "sticky" (they register about ten keystrokes at a time). Sometimes, a keystroke--usually the ENTER key--will cause the entire system to freeze. When this happens, a slight "hum" is sometimes audible through the speakers, and I'm certain it's coming from the Computer Adaptor because I can turn it down with the Adaptor's volume control (a similar hum appears if I try to use the 8914 in place of the 8917). It also happens with my Music Synthesizer keyboard, and during ECS games which use either input device. The extra sound channels and RAM seem to work normally.

 

At first I thought it was just a bad keyboard, but this keyboard tests fine with my second Computer Adaptor, and another known-good keyboard failed in the same way with this Adaptor. I haven't found any visibly bad components or traces, so my best guess at this point is that the 8917 itself is bad. Unfortunately, I haven't yet found a source for a replacement 8917, or a set of pinouts which might allow me to adapt the board for an 8914.

 

Does anyone happen to know if J.H.C. Electronics (the "official" Intellivision repair service) still works on Computer Adaptors? I might have to give them a call if I can't figure this out on my own.

[intvnut]

I apologize I've been silent on this thread. Work swamped me. I'm catching back up though.

 

I just took my ECS apart in an attempt to see what might be different about the pinout, and I must admit I'm stumped. The AY-3-8914 pinout appears to differ from an AY-3-8910 only slightly. Pin 26 is marked as "TEST2" on the AY-3-8910, but is an active-low enable input on the AY-3-8914. Likewise, pins 24 and 25 are enable inputs for the AY-3-8910 and unconnected on the AY-3-8914.

 

I don't know why the AY-3-8917 would need a different pinout than the AY-3-8914. The only thing I can think of is that they needed to do something different with the I/O drivers to support the ECS keyboard or something. (There's a nice array of resistors between the PSG and the controller ports, I'm sure you've noticed.)

 

All the pins I could easily verify (A, B, C analog outputs, the A/B I/O ports, etc.) seem to match what I'd expect from the AY-3-8914 pinout, looking at the AY-3-8917 on my ECS board.

Thanks for looking into this. The 8914 and 8917 looked the same to me, too, which is why I was surprised that I couldn't substitute one for the other. Another member pointed out that some models have different memory maps for the registers, so perhaps this accounts for the incompatibility. I did indeed notice those resistors; in fact, on some Intellivision II consoles, I've seen a similar array of resistors added to the 8914's controller port input pins. My first guess in troubleshooting my Computer Adaptor was to test these resistors with my ohmmeter, and they all checked out (1.5K, I think they are).

 

Perhaps I should describe the problem I'm seeing in more detail. In ECS BASIC or the music player, some keys on the keyboard work normally, some do not work at all, and some are "sticky" (they register about ten keystrokes at a time). Sometimes, a keystroke--usually the ENTER key--will cause the entire system to freeze. When this happens, a slight "hum" is sometimes audible through the speakers, and I'm certain it's coming from the Computer Adaptor because I can turn it down with the Adaptor's volume control (a similar hum appears if I try to use the 8914 in place of the 8917). It also happens with my Music Synthesizer keyboard, and during ECS games which use either input device. The extra sound channels and RAM seem to work normally.

 

At first I thought it was just a bad keyboard, but this keyboard tests fine with my second Computer Adaptor, and another known-good keyboard failed in the same way with this Adaptor. I haven't found any visibly bad components or traces, so my best guess at this point is that the 8917 itself is bad. Unfortunately, I haven't yet found a source for a replacement 8917, or a set of pinouts which might allow me to adapt the board for an 8914.

 

Does anyone happen to know if J.H.C. Electronics (the "official" Intellivision repair service) still works on Computer Adaptors? I might have to give them a call if I can't figure this out on my own.

 

FWIW, I collected up and scanned some ancient data sheets I had that predate the final release of the AY-3-8910. This data sheet says it is for the AY-3-8910, but it seems to offer a more complete pinout, and its register map actually matches the AY-3-8914. I'm guessing that this is probably the most "honest" AY-3-8914 datasheet that I've seen. It even explains what the two envelope select bits in the volume register actually do. (All the other references have only one bit for envelope select, or just say "Put 1 in both these bits.")

 

The scans are here:

 

http://spatula-city.org/~im14u2c/intv/gi_micro_programmable_tv_games/

 

The PSG stuff starts at page 7-100. The rest of it is interesting as an archaeological find, showing how GI conceived the Intellivision system before Mattel bought into it.

 

I guess you've socketed your AY-3-8917? What sort of behavior do you get when you plug in an AY-3-8914? Can you see what, if anything, is hooked to pins 24, 25, 26 and 39? We may be able to make an AY-3-8914 work if it's just a matter of changing the chip selects.

 

 

The memory map issues are, in some sense, a red herring. Both the ECS and Master Component PSGs are mapped at xxF0 through xxFF, and the address bits above that are managed by chip selects (pins 24, 25 and 26), not address lines. Within the xxF0 - xxFF range, both ECS and Master Component PSGs have the same register layout. I should know: My sound effect code treats both identically, just with different base addresses. :-)

[jaybird3rd]

I apologize I've been silent on this thread. Work swamped me. I'm catching back up though.

 

FWIW, I collected up and scanned some ancient data sheets I had that predate the final release of the AY-3-8910. This data sheet says it is for the AY-3-8910, but it seems to offer a more complete pinout, and its register map actually matches the AY-3-8914. I'm guessing that this is probably the most "honest" AY-3-8914 datasheet that I've seen. It even explains what the two envelope select bits in the volume register actually do. (All the other references have only one bit for envelope select, or just say "Put 1 in both these bits.")

 

The scans are here:

 

http://spatula-city.org/~im14u2c/intv/gi_micro_programmable_tv_games/

 

The PSG stuff starts at page 7-100. The rest of it is interesting as an archaeological find, showing how GI conceived the Intellivision system before Mattel bought into it.

 

I guess you've socketed your AY-3-8917? What sort of behavior do you get when you plug in an AY-3-8914? Can you see what, if anything, is hooked to pins 24, 25, 26 and 39? We may be able to make an AY-3-8914 work if it's just a matter of changing the chip selects.

 

The memory map issues are, in some sense, a red herring. Both the ECS and Master Component PSGs are mapped at xxF0 through xxFF, and the address bits above that are managed by chip selects (pins 24, 25 and 26), not address lines. Within the xxF0 - xxFF range, both ECS and Master Component PSGs have the same register layout. I should know: My sound effect code treats both identically, just with different base addresses. :-)

Thanks for that information; very interesting! I'll get the Computer Adaptor out of storage and try it again. I described some of the behaviors I saw when using an AY-3-8914 in place of the AY-3-8917 earlier, but I'll make more detailed notes next time, and I'll also trace out the CS pins to see what they're connected to.