PAL-AT Operating Manual
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Note: If the panel loses power when there are alarms in the alarm queue, the cable status will be “1” (off-
line) after power is restored, until the alarm queue is cleared. The reason for this is the system does not
change the cable status to “2” (normal) while alarms are in the queue. For example, when a leak is
detected the cable status will be “3”. It will remain “3”, even after the new map is created and the system
resumes monitoring and displays “Cable OK”. The system requires an authorized password to
acknowledge the leak event occurred and then it displays the status.
End of Session
If there is more than a 5-minute delay between commands received by PAL-AT, the communication link is
broken and the system address command must be resent. When a communication session is completed
with a specific system, send the address command with system number 255 ("AD,FF") to end the
communication link.
2.10.3 Modbus RTU, TCP, and RTU over TCP
PAL-AT is configured as a Modbus server and can communicate with a Modbus client. PAL-AT supports
function codes 3 and 16 as described below.
PAL-AT can communicate Modbus RTU data to a RS-485 network or RS-232 device via serial ports 1 and
2. In addition, Modbus TCP uses Ethernet port 502 and Modbus RTU over TCP uses Ethernet port 1050.
2.10.3.1 Function Code 3 – Read Registers
Function code 3 can retrieve the cable status value, number of alarms in the alarm queue, and the distance
to a fault for each cable. Refer to the previous section, CS Command, for additional details. The address
is the System Identification (see section 2.9.5). All data is referenced to the start holding register address
of 40001. Each 2-byte register holds data defined in the following manner:
40001 Cable 1 status
40002 Cable 1 number of alarms in the alarm queue
40003 Cable 1 distance or probe number
40004 Cable 2 status
40005 Cable 2 number of alarms in the alarm queue
40006 Cable 2 distance or probe number
40007 Cable 3 status
40008 Cable 3 number of alarms in the alarm queue
40009 Cable 3 distance or probe number
40010 Cable 4 status
40011 Cable 4 number of alarms in the alarm queue
40012 Cable 4 distance or probe number
The cable status values are:
0 = Not installed
1 = Off Line
2 = Normal
3 = Leak
4 = Break
5 = Short
6 = Probe active
7 = Probe reset
8 = Drying
9 = No end/Fault in 1st 50 feet
2.10.3.2 Function Code 16 – Preset Multiple Registers
Function code 16 can remotely clear the alarm queue and allow the relays to reset. To clear the alarm
queue, use function 16 to send hexadecimal AA55 to register 40013. The action is logged in the History
of Events.
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