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Appendix
A.2 Modbus RTU
SENTRON PAC3100
Manual, 07/2009, A5E02385159B-01
127
A.2.3 Function codes
Function codes control the data exchange. In doing so, a function code tells the slave which
action it is to take.
If an error occurs, the MSB bit is set in the response frame in the FC byte.
Supported MODBUS function codes
Table A- 5 Supported function codes
FC Function in accordance with
MODBUS specification
Data Type Access
02 Read Discrete Inputs Bit Input R
03 Read Holding Registers Register Output R
04 Read Input Registers Register Input R
06 Write Single Register Register Output RW
10 Write Multiple Registers Register - RW
2B Read Device Identification - - R
FC 02
This function code reads individual bits from the slave.
Corresponding exception codes: 01, 02, 03 or 04
Corresponding error code: 0x82
0 = OFF
Status:
1 = ON
FC 03
You can read out device registers with this function code.
Number of requested registers: At least 1 to maximum 125
Corresponding exception codes: 01, 02, 03 or 04
Corresponding error code: 0x83
FC 04
You can read out device registers with this function code.
Number of requested registers: At least 1 to maximum 125
Corresponding exception codes: 01, 02, 03 or 04
Corresponding error code: 0x84