Alesis QS7.1 User Manual download pdf (Page 12)

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:

DD0-DD7

Data Buss bits 0 to 7. Correspond to the upper 8 data bits of the H8.

H8 Address Buss bit 0

H8 ReaD enable

H8 WRite enable

KEY

Chip select line from GAL (Mapped I/O)

KEYINT

Output to H8 interrupt line

KEYCLK

Clock input from H8

ROW0-7

Row input from keyboard switch matrix

COL0-21

Column input from keyboard switch matrix

VSS1-4

Source Supply (GND)

VDD1-4

Drain Supply (+5V)

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

1 2 ... 7 8 9 10 11 12 13

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Alesis QS7.1 User Manual Page 12