7 Pot
Panel
7.1
Theory of Operation
The Pot Panel serves two major functions:
Keyboard Interfacing. The VPK-5 keyboard clock/power signal is
generated under control of the CPU. The keyboard digital data is
detected and sent to the CPU. The keyboard analog data is
demultiplexed and routed to the DIGIMOD card.
Parameter Trimmer Interfacing. The Parameter Trimmers are multiplexed
and routed to the DAC card for digitizing.
7.2
Keyboard Clock/Power Interface
The CPU card controls the keyboard by sending commands on the
power line that drive the keyboard circuitry (see KEYBOARD THEORY
section.) The 74LS138 U1 is controlled by the CPU via the address bus
selection of one of eight outputs. These functions are:
•
Demultiplexer
Enable
(DEMUXEN): The CPU uses this line to
turn on the CD4051 system demultiplexers. When a CD4051 is to
be written to, the CPU writes to the 74LS138 position 3, which
sets flip-flop 74LS279 LOW. When done, the CPU writes to
location 4 and sets the flip-flop HIGH. This DEMUXEN line drives
a 16 channel demultiplexer on DIGIMOD that drives all of the
system CD4051s. In normal operation, the DEMUXEN line should
always be active,
i.e.
pulses should always be present since the
CPU will always be refreshing the system CD4051s.
•
Clock
(CLK): The Keyboard needs a clock signal to shift the
digital data through the parallel-to-serial converters that are
connected to the contacts (see Keyboard Theory of Operation.)
When the CPU wants to access this data, it writes to the 74LS138
position 0.
•
Digital Strobe (DSTR): When the CPU needs digital data from the
keyboard, it generates a strobe pulse to set the keyboard logic to
digital access mode. This is done by writing to 74LS138 position 1.
•
Analog Strobe (ASTR): When the CPU needs analog keyboard
data, it generates this strobe and toggles the keyboard logic to
analog mode. This is done by writing to 74LS138 position 2. When
in analog access mode, the circuitry that follows the 74LS138
automatically generates a slower analog clock.
