Ursa Major Space Station SST-282, 82S123 replacement

How to make a replacement for the 82S123 ROM chip (ADS-1 board – U19) in Ursa Major Space Station SST-282, using an 22v10 Programmable Logic chip and a cheap EPROM programmer.

I used Atmel ATF22v10CQZ-20PU and the common TL866iiPlus.

This is not a step-by-step guide, you are expected to know how to use an EPROM programmer.

Main SST-282 main image
Two Space Stations in for service, one with a problematic 82S123

What is the N82S123N chip

The Space Station doesn’t have a processor, but you can still select different reverb-, filter- and delay algorithms. This is achieved with hardware buttons that make the 82S123 IC output various control signals to the rest of the machine.

Two M82S123N chips from the SST-282
82S123 from the two Space Stations above

The 82S123 is not an ordinary EPROM, it’s a bipolar TTL PROM. It is way faster than EPROM, with response times in the nanoseconds. You can get them NOS on eBay. The problem is that an EPROM programmer that supports this type of chip is expensive.

I haven’t verified this, but these chips should be direct replacements for the 82S123:
7112, 27S19, 6331-1N, 74S288, 18S030, 7603

The ATF22v10C Programmable Logic IC

Atmel F22v10CQZ-20PU and little brother F16v8BQL-15PU

The ATF22v10 is a Programmable Logic chip, made by Atmel. Other brands are sometimes called PAL chips. ATF / PALs are much more flexible than EPROMS, mainly because you can run small programs on them, so they behave differently depending on signals present on the input pins. They are also very fast, and that’s why they are fit to replace an 82S123.

So in short, I needed the 22v10 to output one of 32 numbers, depending on the state of its input pins – just like a small EPROM.


Luckily I found someone that made a 82S123 replacement using the GAL22v10D, which is “practically the same” chip: REPROGRAMMABLE 82S123. Beware though that not all EPROM programmers and ATF / PAL / GAL chips are compatible.

So I read a bit of documentation on 22v10, as well as the programming language (CUPL Compiler for Universal Programmable Logic) and tool (WinCUPL)

Hardware adapter

22v10 is a 24-pin chip, whereas 82S123 is only 16-pin, so an adapter is needed. Please refer to this site for detailed information: REPROGRAMMABLE 82S123

My version looks like this

82S123 socket to 22v10 IC adapter top
82S123 socket to 22v10 IC adapter bottom

Programming the Space Station data to 22v10

You need an EPROM programmer that is compatible with the 22v10 brand that you have


Ursa Major Space Station with the new ATF22v10C added


“Why not use the smaller 16v8 PAL instead? It’s smaller but it has enough pins…”

Well, if you try to compile any code that contains a 32 byte ROM table and the necessary pin bindings in WinCUPL it’s going to fail. WinCUPL even outputs a nice Word document that shows exactly where the resources are exhausted.