ALESIS QS SYNTHESIZERS UNOFFICIAL REPAIR GUIDE
2.34 THE KEYSCAN ASIC
While the task of polling the keyboard may seem difficult at first (up to 88 Keys with velocity), the Keyscan ASIC takes
care of this task and passes the information back to the H8 processor . The main signals of the Keyscan ASIC are:
Data Buss bits 0 to 7. Correspond to the upper 8 data bits of the H8.
Chip select line from GAL (Mapped I/O)
Output to H8 interrupt line
Row input from keyboard switch matrix
Column input from keyboard switch matrix
2.34A READING VELOCITY
Velocity response is measured through the time differential between two switch closures and works like this:
FIGURE 4 - KEYBOARD VELOCITY REPONSE
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