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P72x/EN CT/A11
Communication database
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MiCOM P721/P723
2. MODBUS
PROTOCOL
MiCOM P721
and
P723
relays can communicate by a RS 485 link behind the unit following
the MODBUS RTU protocol.
2.1
Technical characteristics of the MODBUS connection
2.1.1
Parameters of the MODBUS connection
The different parameters of the MODBUS connection are as follows:
−
Isolated two-point RS485 connection (2kV 50Hz),
−
MODBUS line protocol in RTU mode
Communication speed can be configured by an operator dialog in the front panel of the relay:
Baud rate (dec)
300
600
1200
2400
4800
9600
19200
38400
Transmission mode of the configured characters by operator dialog
Mode
1 start / 8 bits / 1 stop: total 10 bits
1 start / 8 bits / even parity / 1 stop: total 11 bits
1 start / 8 bits / odd parity / 1 stop: total 11 bits
1 start / 8 bits / 2 stop: total 11 bits
2.2
Synchronisation of exchanges messages
A character received after a silence (
≥
3 characters transmission time) is considered as a
frame start.
2.3
Message validity check
The validation of a frame is performed with a 16-bit Cyclical Redundancy Check (CRC).
Generator polynomial: 1+x²+x
15
+x
16
= 1010 0000 0000 0001 (binary) = A001 (hexadecimal)
2.4
Address of the MiCOM relays
The address of the MiCOM relay on a same MODBUS network is situated between 1 and
255. The address 0 is reserved for the broadcast messages
Summary of Contents for P721
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Page 15: ...Introduction P72x EN IT C21 MiCOM P721 P723 INTRODUCTION...
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Page 299: ...Connection Diagrams P72x EN CO A11 MiCOM P721 P723 CONNECTION DIAGRAMS...
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