9: Processor Board
9-4
PRC1099A-MS
9.1.8
Control Bus Outputs
Control bus outputs PA2 through PA7 provide serial programming
information to the other radio boards. This bus includes synthesizer select
signals, data and clock signals along with filter and tuner signals. The control
bus also outputs the display information to the Display board.
9.1.9
Control Outputs
The control outputs from serial shift register U15 control the following
devices:
• Tune initiate from the front panel.
• Enable and shutdown signals to the RS-232 chip.
• AGC time constant switching.
• Display backlight on/off control.
• External amplifier PTT enable.
• ALE Board switch.
9.1.10
EEPROM Memory
Serial EEPROM memory chip U18 stores critical operating settings necessary
for proper radio operation.
9.1.11
Input Demultiplexer
Input demultiplexer U14 interfaces the 16 input lines to the processor. Analog
multiplexer/demultiplexer U14 has 16 channels and four address lines. The
processor communicates with the input demultiplexer through the d-mux bus.
The five-line D-mux bus consists of four address lines connected to PA10
through PA13 from the processor and an input line connected to PA14. The
processor outputs the desired input channel address through the address lines,
and data is read in through the input line.
9.1.12
Wake-Up Control
State-change detector U12 represents half of the wake-up control block. It
monitors the input lines for any change in the state of the inputs, then triggers
an interrupt to the processor. U12 is an MC14531 12-bit parity tree with 12
inputs, odd/even parity-select input and a parity valid output. The interrupt
signaller U13 is an MC14528B dual-monostable multivibrator. One section of
the multivibrator is configured to trigger on the rising edge of the parity tree
input and the other on the falling edge. The outputs of the multivibrators drive
the interrupt line of the processor, which then bring the processor out of the
standby state.
