Modbus Interface; Communication Link; Modbus Functions; Response Codes - GE MiCOM P40 Agile Technical Manual

P44x/EN SC/Hb6
(SC) 12-20
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
02
03
04
06
08
11
12
16
These are interpreted by the MiCOM relay in the following way:
01
02
03
04
06
16
3.3

Response codes

Code
01
02
Read Coil Status
Read Input Status
Read Holding Registers
Read Input Registers
Preset Single Register
Diagnostics
Fetch Communication Event Counter
Fetch Communication Event Log
Preset Multiple Registers 127 max
Read status of output contacts (0xxxx addresses)
Read status of opto inputs
Read setting values
Read measured values
Write single setting value
Write multiple setting values
MODBUS Description
Illegal Function Code
Illegal Data Address
SCADA Communications
MiCOM P40 Agile P442, P444
(1xxxx addresses)
(4xxxx addresses)
(3xxxx addresses
(4xxxx addresses)
(4xxxx addresses)
MiCOM Interpretation
The function code transmitted is not supported by
the slave.
The start data address in the request is not an
allowable value. If any of the addresses in the