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30. P725 to P725 Serial Links
Local And Remote Systems Linked Via Communications
In applications that require local panel alarms to be duplicated or summarised in central control
rooms or monitoring stations the P725 can be supplied with a communications option which allows
RS485 communication using Modbus protocol as standard between units. In this application the local
annunciator is directly wired to the alarm contacts in the normal way but the alarm information is also
made available to transmit over the RS485 communications link to a 2
nd
P725 unit mounted in the
control room or monitoring station.
RS485 LINK BETWEEN
P725 ANNUNCIATORS
SLAVE
MASTER
All systems supplied with serial communication cards are automatically equipped with integral
watchdog relays, which will change state if any errors in the internal or external communication are
detected. In larger schemes multiple remote P725 Annunciators, each with serial communications,
can be connected to a single P725 used for central monitoring. The key advantage with units
configured in this manner is the central monitoring annunciator only requires 24VDC logic power and
a 4 core RS485 cable to function. In this example functions F16 and F17 are used to configure each
unit to either transmit or receive serial data as required. Local panel units are hard wired to the
associated field contact and once configured transmit alarm data over the serial communication link.
Please note:- one of the devices must be set as a master.
Communication Link Wiring Details
8
7
6
5
5
6
7
8
5
6
7
8
5
6
7
8
SCR
RXa
RXb
TXa
TXb
TXb
TXa
RXb
RXa
TXb
TXa
RXb
RXa
P725 MASTER
P725 SLAVE
P725 SLAVE
