18 Sep
2007
18 Sep
'07
11:58 p.m.
If the 40-pin DIP on the board does not have Vcc and GND connected to
"corner" pins (40 and 20, respectively), it's probably one of the
'standard" keyboard chips by GI or NSC. The MM57499N that I
mentioned was very common in terminals in the late 70s and the early
80s. Directly addressed a keyboard matrix with 2-key rollover, had
LED output pins and serial output interface. But the power on both
GI and NSC keyboard chips were at "non-corner" pins, such as 5 and
22.
During the aforementioned time, uC's like the 8048/8051 were fairly
expensive, particularly when compared to a "for purpose" IC.
Just guessin',
Chuck