Function Code Support - rotork Modbus Technical Manual

Modbus MFU Option Card Installation Manual

7.3 Function Code Support

Details of the Request and Reply formats for messages can be found in the Modbus Application
Protocol Specification V1.1b3, found at http://www.modbus.org. The following table lists the function
codes supported by the Modbus Module.
Function
Code
01 Read Output Coil Status
02 Read Input Status
03 Read Holding Registers
04 Read Input Registers
05 Force Single Coil
06 Preset Single Register
07 Read Exception Status
08 Loopback Diagnostic Test
15 Force Multiple Coils
16 Preset Multiple Registers
17 Report Slave ID
Exception Response
Code
01
02
03
06
To read data the function code to use will depend on whether the data is to be read as single bits or as
16 bit registers. For example, code 01 reads data as discrete bits, whereas code 03 reads the data as
registers. In many cases Discrete and Register access reads the SAME data.

Code 01 - Read Coils

Code 02 - Read Input Status Requests

Code 03 - Read Holding Register Requests

Code 04 - Read Input Register Requests
42 of 64
Modbus Name
Illegal function code or incorrect message length
Illegal data address (Register or discrete address invalid)
Illegal data value
Busy
This is used to read discrete (bit) data from the database to obtain
information about the status of the output coils (commands).
This is used to read discrete (bit) data from the database to obtain
information about the actuator current status, such as open or closed
positions reached.
All the data in the MFU can be read using function code 03. Discrete
data is mapped into registers that are available for this command.
Actuator position and torque registers, plus the status bits are
accessible with function code 04.
Publication PUB091-004-00_0918
Addressing
Meaning
Discrete
Discrete
Register
Register
Discrete
Register
Discrete
Register