b6
-20 MiCOM P40 Agile
3 MODBUS INTERFACE
The MODBUS interface is a master/slave protocol and it is defined by MODBUS.org: See
www.modbus.org
MODBUS Serial Protocol Reference Guide: PI-MBUS-300 Rev. E
3.1 Communication link
This interface also uses the rear EIA(RS)485 port (or converted fiber optic port) for
communication using ‘RTU’ mode communication rather than ‘ASCII’ mode as this provides
more efficient use of the communication bandwidth. This mode of communication is defined
by the MODBUS standard.
In summary, the character framing is 1 start bit, 8 bit data, either 1 parity bit and 1 stop bit, or
two stop bits. This gives 11 bits per character.
The following parameters can be configured for this port using either the front panel interface
or the front Courier port:
• Baud rate
• Device address
• Parity
• Inactivity time
3.2 MODBUS functions
The following MODBUS function codes are supported by the relay:
01 Read Coil Status
02 Read Input Status
03 Read Holding Registers
04 Read Input Registers
06 Preset Single Register
08 Diagnostics
11 Fetch Communication Event Counter
12 Fetch Communication Event Log
16 Preset Multiple Registers 127 max
These are interpreted by the MiCOM relay in the following way:
01 Read status of output contacts (0xxxx addresses)
02 Read status of opto inputs (1xxxx addresses)
03 Read setting values (4xxxx addresses)
04 Read measured values (3xxxx addresses
06 Write single setting value (4xxxx addresses)
16 Write multiple setting values (4xxxx addresses)
3.3 Response codes
Code MODBUS Description MiCOM Interpretation
01 Illegal Function Code
The function code transmitted is not supported by
the slave.
02 Illegal Data Address
The start data address in the request is not an
allowable value. If any of the addresses in the
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