computer

The touch control was imple- mented with toggle switches mounted on the keys. The time needed for toggling was detected as a measure for the power of the keystroke. The particular challenge was, that the switches had to be scanned with at least 1 kHz for an appropriate resolution, but the 1 MHz 6502 CPU was too slow to perform the scan of 76 keys. We solved that problem with a self developed controller which scanned the keyboard and put op-codes on the CPU's data bus, in realtime: a "NOP", when a key didn't need any attention, a call to the suitable subroutine (e.g. increment of counters) otherwise. (-)