Specifications

Engineering Standard –NSW
Signalling SMS 02
Cerberus Level Crossing Monitor Equipment
March 2005 Version 1.2 © Australian Rail Track Corporation Page 26 of 118
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Continuously repeat the following at 0.25 second intervals: Turn led 4
on.
Check Real Time Clock.
Kick over watch dog.
Scan inputs, update state, and log changes.
Scan timers, update state, log changes, and every fourth time
update run time.
As necessary and every fourth time:
Evaluate expressions.
Scan outputs, log changes, and write outputs.
Scan analogue inputs, update status, and log
changes. Every fourth time.
If not maintenance disabled and their has been a status change
then store the time of the change and set the status to report flag
for task 1.
If their is a communications link on serial port A and there has not
been a valid message sent or received for the last 10 minutes then
force the modem to be hung-up.
Log changes in serial port
connections. Turn led 4 off.
Serial communications task description
Execution of this task is commenced by task 1. It then proceeds in
the following manner:
Initialise variables.
Continuously repeat the following:
If a serial port interrupt has occurred then
Acknowledge the interrupt to the Serial Controller
Chip. Read the Serial Controller Chip interrupt status
register.
Repeat the following until their are no more interrupts to be
processed.
1. If a serial port A receive interrupt occurred then turn led 5 on,
check for and process any reception errors, and process the
received character.