Miteq D-9301, Operation And Maintenance Manual, Page: 48 / 86

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4.3.3 CONVERTER CONTROLLER
The Converter Controller board contains the microcomputer and
analog circuitry necessary to control the LCD display, accept
data from the front panel keys, control the frequency
synthesizer, monitor status signals from the critical converter
components, control the muting and alarm relays and provide a
remote bus interface (e.g. RS485).
The microcomputer is designed with a microprocessor which
contains on-chip RAM, a serial port and an I/O port. Program
memory is stored in an EPROM. Additional RAM is located on a
peripheral IC along with extra I/O ports and a timer. The I/O
ports read the rear panel DIP switch for address and baud rate
selection (remote bus option only), control the "MEMORY" and
"REMOTE" front panel LEDs, control the muting and alarm relays
and monitor the analog status alarm circuitry. The on-chip timer
is used as a gated oscillator to sound the buzzer.
The I/O port on the microprocessor controls the LCD controller
chips, stores and recalls data from the EEPROMs (non volatile
memory) and sends serial data to the frequency synthesizer via
the interface ICs. When the remote bus option is used, the
microprocessor on-chip serial I/O port is used with the interface
ICs to provide an RS422/485 interface.
Front panel keys are monitored by the keyboard encoder. The keys
are scanned at a periodic rate and an interrupt is generated
whenever a key is pressed. Key debouncing and multiple key
lockout are also provided in the chip.
The power monitor IC performs three functions. A power on reset
pulse is generated whenever power is turned on. As a power
monitor, it continuously monitors the +5V power supply and
generates a reset signal if the supply drops below 4.5V. It also
contains a watch dog timer which must be periodically reset by
the microprocessor. Failure to do so indicates a circuit failure
and causes a reset pulse to be generated.
The analog section monitors signal levels from the critical
converter components and outputs to the microcomputer whenever a
fault level has been reached. Fault levels for the power
supplies are fixed while others such as the LO level detect are
adjusted with trim pots. A separate relay, DC alarm, is
controlled from the output of the power supply monitor circuitry.
The two front panel alarm LEDs, "RF-LO" and "IF-LO", are
controlled from the analog circuitry.