Sequential prophet 5 - Matrices

2-13 CONTROL PANEL MATRICES
This paragraph describes how the computer "scans” the control panel to learn what keys or switches
have been pressed, and to light the LEDs imbedded in switches (that are ON".) figure 2-8 block-
diagrams the control panel. You may also want to consult the schematic. SD212 (page 3-11).
A matrix is an area of signal lines with devices connected diagonally where they cross. SD212 clarifies
the arrangement. Consider the keyboard matrix first. One side connects to SWITCH DRIVER latches
U209/12. the other to drivers U204/5. (Bus drivers are functionally similar to latches. When clocked,
they place data on the bus.) To read the keyboard, the CPU places the number 00000001 on the bus,
and supplies CS8. The SWITCH DRIVERS hold the first matrix line, DX0. high. Whatever keys in the
row are held will place 1 on their connecting columns, DY0 - DY7. For example, if DO is held, the
number 00000100 will be driven on to the bus when -CSE appears. (If more than one key in a row is
held, the CPU subtracts to find the actual combination.) After reading row DX0, the CPU activates
row DX1 with the number 00000010. and CS8. and reads the matrix output again with -CSE.
The matrix diodes prevent switched bits from returning through other closed switches on the same
column, which would activate other rows.
Control switches are read in the same manner as the keyboard switches, except using another driver
clock. -CSD.
To light the switch LEDs, one row is activated low through inverters, and the LED DRIVER latches
U208/11 supply the necessary high signals. The LEDs are therefore not constantly lit. they only seem so
due to persistence effects accompanying our sight.
For PRESET operation, data representing selected switches and their corresponding LEDs is read from
the NV PRGM RAM.
2-16