Sequential PROPHET-600 - 7-7 AMPLIFIER

from +5-V to + 15-V level. The corresponding destination switches operate at higher
voltage to accomodate high-level synthesizer signals. These four signals, and the three
unshifted switch signals each have six destinations: one analog switch on each voice.
2-11 DAC and CV DEMULTIPLEXER
In addition to providing switch signals, the computer of course provides CVs to the
synth, in the following way.
Refer to Sheet D. U32S, clocked by -DAC HI, latches the six most-significant (MS)
DAC bits. U327 and U324 form the latch for the eight LSBs, clocked by -DAC LO. The
MS latch is always used, but the LS latch is only used to provide the resolution needed
for oscillator frequency CVs. The fourteen latched DAC bits cross over from TB303 on
PCB 3 to drive the DAC on PCB4. See Sheet E. U40I-U403 buffer the bits and invert
them to the activq-low inputs which U405 DAC requires.
The DAC has a basic range from 0 to 4.9V, adjusted by R4333. (This trimmer is not
used on early production units which have a Burr-Brown DAC71.) U414 converts the
output current to voltage, Vdac.
During each interrupt cycle Vdac assumes the value of each S/H, and of the wheel and
control which are being read. The CV demultiplexer (DMUX) is synchronized so that
Vdac strobes the correct S/H at the precise time that it assumes the corresponding
value. Figure 2-6 shows Vdac.
V: lV/div
H: .2 ms/div
Figure 2-6
VDAC, FACTORY PROGRAM 00
2-12
TM600A 7/83