Tek 11A34 with piggyback CPU

[PA0PBZ]

Look at this, found it inside a Tek 11A34 4 channel plug-in amplifier. It's not even a pre-production one, the serial says B020837.
Why would they use this, it must cost so much more than a normal OTP 83C154. Or OKI got stuck with a bunch of these and they got a special deal, I don't know. But it is remarkable, you don't really see these piggyback CPU's in normal equipment.

[mikeselectricstuff]

Maybe OTPs weren't available - I'm sure there were some parts where the only choice was piggyback or maskrom. May also have been to allow easier firmware updates without needing a special programmer.

[SeanB]

Most likely they were going to go for a OTP version, but did not have the projected numbers to get the cost down or they got a good deal on the piggyback version so they could use it in a number of boards and not have an expensive single use part, just a cheaper multiuse part that could be customised with a simple cheap rom added to it. Probably used as it saved the space of the micro, the rom, the ram and the 4 glue logic and bus buffer chips that would otherwise be needed. The space was worth a lot more than the piggyback package, it would probably have involved a mezzanine board on top of all the others with a connector to join them.

[BravoV]

Amazing device, btw, does that DS1220Y still alive holding it's memory ? That thing is 26 years old now. 

[SeanB]

Probably has had the low battery flag on for around 5 years I would guess, but still has enough left to stay alive. Not likely that the flag is read.

[PA0PBZ]

Maybe OTPs weren't available - I'm sure there were some parts where the only choice was piggyback or maskrom. May also have been to allow easier firmware updates without needing a special programmer.

Can't find it again of course, but in an OKI datasheet it was described as "the development version of the OTP 83C154, so they must have at least planned to have an OTP version. Not sure if it was easier/cheaper to do a firmware update this way or just replace the OTP, depends on the price of both devices and the number of updates of course.  It does not really look like an early stage of the software, this one has version 3.6, another plug in I have with the (OTP/Mask?) 83C154 has version 3.7 in it.

Well, having said that, it looks like even that version came as a piggyback one time:



I still have too many D8741's which are 'normal' dips with an erase window in it, still can't bring myself to throw them away:

Amazing device, btw, does that DS1220Y still alive holding it's memory ? That thing is 26 years old now.

Probably has had the low battery flag on for around 5 years I would guess, but still has enough left to stay alive. Not likely that the flag is read.

It's guaranteed for 10 years, it sure lived up to that promise. The DSA is still not complaining, so I'm in doubt if I should decap them and replace the battery.

[SeanB]

Must open the eprom eraser and see what is lurking inside there aside from the ZN1034e timer.

[mikeselectricstuff]

Could have been as simple as they used the piggyback for development and/or early production, it got put in the BOM and nobody bothered to change it later.
Could also be that they had some system set up for managing firmware etc. and using a standard EPROM fitted more easily into that system. Also means service centres and/or production programming facility didn't  need a special programmer.