B&R Introduction of MODBUS communication function block

Open the help file of B&R, search for DRV_MBUS, you can find the DRV_MBUS library.

In the figure above, you can see the functional blocks related to MODBUS communication, there are 4 functional blocks related to the master station, and 3 functional blocks related to the slave station. B&R mainly uses the following function blocks as the master station.

a. MBMOPEN()

The MBMOPEN() function block opens (activates) the master communication interface. The parameters are as follows

I/O parameter Meaning

I enable function block enable

I PDEVICE Name of the communication interface

I PMODE Communication interface parameter setting

The name of the IPCONFIG data block

I timeout communication timeout parameter

I ascii MODBUS mode, (0=RTU/1=ASCII)

O status error code, 0 means no error

O IDENT The handle provided to MBMaster(), MBMCmd(), MBMClose()



b. MB Master()

I/O parameter Meaning

I enable function block enable

I ident Handle pointer returned from MBMOpen()

O status error code, 0 means no error

O execute Whether to execute the command

O recordnum The number of current data exchange



c.MBMCmd()

I/O parameter Meaning

I enable function block enable

I ident Handle pointer returned from MBMOpen()

I mfc Modbus function code

I node Slave station number, 0 is broadcast

I data Data area first address

I offset offset

I len data length

O status error code, 0 means no error



d. MBMClose()

Close the communication interface of the master station

I/O parameter Meaning I enable Function block enable I ident Handle pointer returned from MBMOpen() O status Error code, 0 means no error