Also found this on line
Micro Switch Keyboard it has a 28pin encoder chip were mine has a 40pin, but same prefix (SW) not sure on the woodwork.
This
Doc on Diablo HyTerm model 1620 also looks interesting on page 2-36 and on its talk about the 2-of-13 encoding that is accomplished on the circuit board using the MOS decoder/encoder chip, and chip info on 4-57.