Sequential PROPHET-600 - 7-6 ENVELOPE GENERATORS

2-9 SWITCH MATRIX
The matrix switch scanning method is also widely used. Strobe CSOO is used to latch
four-bit numbers to decoder U104. This <*51 sequentially applies high voltages to each
row of switches in the matrix (connected to S0-S15). Figure 2-5 shows two of these
strobes.
V: IV/div
H: 2 ms/div
Figure 2-5 A B
STROBES SO SWITCH S8 KEYBOARD
The -CSI1 (Chip Select Input) strobe then enables U105/U106 bus drivers, which place
the data coding held switches in the current row on to the bus.
SA2 keyboard is the most obvious switch array. Each key is actually a SPST
momentary switch. The diodes wired throughout allow n-key rollover (the pressing of
any number of keys) by isolating each switch. If the diodes were not present, signals
from closed switches would pull other rows high.
The switch elements of SAI membrane panel are also SPST momentary but arc not
protected from n-key rollover by diodes. Instead the whole pad is isolated from the
rest of the matrix by D101 - D108.
Because the synthesizer switches are slide (rather than having LEDs), they can't show
their programmed position, except by being toggled. One switch on PCB 2 is wired into
this part of the matrix (see sheet B, SD600-2).-
2-10 SWITCH LATCHES
We have seen data latched off the bus to drive the LED matrix, and to provide strobe
signals for the switch matrix. The signals which control analog switches in the
synthesizer form a third type of output. In Preset mode these switch signals are set by
the current program. In Edit or Manual Modes these signals directly follow their
corresponding switch on the control panel.
See Sheet D (SD600-3, 2/2). It was already mentioned above that latch U331 is held
reset during power up, to discourage random sounds. In normal operation, data for this
latch is strobed with -CS03. The seven signals cross over TB305 to (turn to Sheet E,
SD6Q0-4, 1/4). Following TB404 (to the right), U404 shifts four of the switch signals
TM600A 7/83
2-11