Communication instructions Chapter 9
Rockwell Automation Publication 2080-RM001D-EN-E - February 2015 197
MSG_MODBUS sends a Modbus message over a serial port.
MSG_MODBUS operation
A maximum of four message requests per channel can be processed in one scan.
For Ladder Diagram programs, message requests are executed at the end of a
ladder scan.
Arguments
Parameter
Parameter
type
Data type Description
IN Input BOOL If Rising Edge (IN turns from FALSE to TRUE), start the function block with the
precondition that the last operation has been completed.
Cancel Input BOOL TRUE - Cancel the execution of the function block.
LocalCfg Input MODBUSLOCPARA Define structure input (local device).
Defines the input structure for the local device.
See MODBUSLOCPARA data type on page 199.
TargetCfg Input MODBUSTARPARA Define structure input (target device).
Defines the input structure for the target device.
See MODBUSTARPARA data type on page 204.
LocalAddr Input MODBUSLOCADDR MODBUSLOCADDR is a 125 Word array that is used by Read commands to store
the data (1-125 words) returned by the Modbus slave and by Write commands
to buffer the data (1-125 words) to be sent to the Modbus slave.
Q Output BOOL
Outputs of this instruction are updated asynchronously from the program scan.
Output Q cannot be used to re-trigger the instruction since IN is edge
triggered.TRUE - MSG instruction is finished.
FALSE - MSG instruction is not finished.
Error Output BOOL TRUE - When error occurs.
FALSE - No error.
ErrorID Output UINT Show the error code when message transfer failed.
See Modbus error codes on page 199.
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