“A long time ago, 7400 logic was all that was available, but having only 7400 logic means designs can get big and difficult, but making a custom logic IC was expensive and hardly a possibility. A few companies started making programmable logic devices like the Programmable Logic Array (PLA) and Programmable Array Logic (PAL). These devices started being available in the 1970’s and where generally one time programmable devices, with the capability to contain a handful of simple logic. Much later, in 1985, the Generic Array Logic (GAL) came into existence, a reprogrammable version of the PAL. Later on the CPLD’s and FPGA’s came and are still used today.When reading about this I discovered there are still GAL’s made and sold, and getting old ones from Ebay is easy enough. They looked like weird odd devices, so I decided to have a closer look, eventually making a dual BCD to 7 segment decoder with them that even handled multiplexing.
What’s inside a GAL
The GAL I ordered is the GAL22V10. The chip number directly says something about it, 22V10 means it has 22 IO’s from which 10 can be used as an output. The 16V8 for example has 16 IO’s from which 8 can be used as output.”