Mbus_Msg / Mb_Msg2 Instruction - Siemens SIMATIC S7 System Manual

9.3.2.3

MBUS_MSG / MB_MSG2 instruction

MBUS_MSG and MB_MSG2 have identical behavior and parameters. MBUS_MSG is for a
single Modbus RTU master. MB_MSG2 is for a second Modbus RTU master.
Table 9- 5 MBUS_MSG / MB_MSG2 instruction
LAD / FBD STL
CALL MBUS_MSG, First, Slave,
RW, Addr, Count, DataPtr,
Done, Error
CALL MB_MSG2, First, Slave,
RW, Addr, Count, DataPtr,
Done, Error
The MBUS_MSG / MB_MSG2 instruction initiates a master request to a Modbus slave when
both the EN input and the First inputs are ON. Sending the request, waiting for the response,
and processing the response usually requires several PLC scan times. The EN input must
be ON to enable the send request, and must remain ON until the instruction returns ON
(True) for the Done bit.
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
Description
The program calls the MBUS_MSG / MB_MSG2 instruc-
tion to initiate a request to a Modbus slave and process
the response.
Libraries
9.3 Modbus RTU library
483