Technical Guide P92x/EN FT/E11
User Guide
MiCOM P921-P922-P923 Page 35/110
9. COMMUNICATION
9.1 Rear communication port description
The rear communication port is provided by a 3-terminal screw connector located on
the back of the relay.
The rear port provides RS485 serial data communication and is intended for use with
a permanently-wired connection to a remote control centre. Of the three connections,
two are for the signal connection which can be connected either way round, and the
other is for the earth shield of the cable.
The rear RS485 interface is isolated and is suitable for permanent connection
whichever protocol is selected. The advantage of this type of connection is that up to
32 relays can be ‘daisy chained’ together using a simple twisted pair electrical
connection.
All the connections are described in details into the Chapter 2 of this Technical
Guide.
9.2 Rear and front communication management
9.2.1 Modification through the front panel
If there is any modification of the settings done through the front panel, a
downloading of a new settings file via the MiCOM S1 software (locally), or via a
remote master station will be forbidden.
The change of settings will be possible as soon as the setting mode will elapse (at the
end of the 5mn timer or after power off/power on of the relay).
9.2.2 Modification through the MiCOM S1 software (front port, RS232)
If there is any modification of the settings through the MiCOM S1 software, a
modification through the front panel will be forbidden and the following message will
appear :
Write lockout
9.2.3 Modification through the rear port (RS485)
If the user is trying to access simultaneously to the settings of the relay through the
RS232 and RS485 communication ports, there will be no messages on the display of
the MiCOM relay : the last modifications will be taken into account without any
warning.
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