and key down information is determined by the Chip Select (CS) lines CS
UB (for Upper Bus, or Key Up) and CS LB (for Lower Bus, or Key Down).
Again, since the CPU will always be accessing the keyboard, these lines
should always be active.
7.3.2 Analog Data Retrieval
The buffered keyboard data is also routed to the analog demultiplexing
circuitry comprised of CD4051 U14, CD4024 U8 and CD4051 U7 with
associated subcircuits. The CD4024 is clocked by the same circuitry that
generates the keyboard analog clock and uses the CD4051 U7 to
generate an ENable pulse to drive the CD4051 U14 synchronously with
the keyboard analog data that is being received. This analog data, which
may have both positive and negative transitions, is demultiplexed and
buffered at the U14 outputs and processed for use in the analog portions
of the VOYETRA. Since the CPU will always be scanning the keyboard
analog data, the control signals on these ICs should always be active in
normal operation.
7.3.3 Controllers
The Pitch Bend (Joystick Y axis), +/- X joystick and pressure controllers
that are demultiplexed by U14 are further processed by the analog
circuitry that follows the LM324 U16 buffers. The CD4053 switches allow
the VOYETRA to be controlled by a slave when they are switched to the
“external” positions. This is set by the CTRL KBD line that comes from
DIGIMOD. Also, Pitch Bend for the Left and Right sides of the VOYETRA
can be turned off with the CD4053 switches that precede the U17
inverters. The pressure controller is buffered and sent to DIGIMOD. The
+/- X controller is split into +X and –X, then sent to DIGIMOD.
7.4 Parameter
Trimmer
Multiplexer
The CD4051s U20 and U21 are used to multiplex the front panel
potentiometers. The CPU selects the pots by controlling the CD4051
positions via the Pot Data (PD) lines PD0, PD1, PD2 and PD3 that are
generated on DIGIMOD. The multiplexed pot information (PANALOG) is
routed to the DAC card and digitized for use by the CPU. Since the CPU
constantly scans the pots in normal operation, the PANALOG and PD
lines should be dynamic signals.
7.5
Master Volume and Master Tune Controls
The Volume Control has no active circuitry associated with it. The pot
derives its voltage and ground from the jack bay where it is processed
and routed to the MIXER card. The Master Tune pot is routed to the pitch
bend buffers and is used to transpose the entire instrument uniformly.
