105BCommunication processor
12.5 Modbus communication
S7-1200 Programmable controller
600
System Manual, 11/2011, A5E02486680-05
12.5.3.1
MB_COMM_LOAD
Table 12- 63 MB_COMM_LOAD instruction
LAD / FBD
SCL
Description
"MB_COMM_LOAD_DB"(
REQ:=_bool_in,
PORT:=_uint_in_,
BAUD:=_udint_in_,
PARITY:=_uint_in_,
FLOW_CTRL:=_uint_in_,
RTS_ON_DLY:=_uint_in_,
RTS_OFF_DLY:=_uint_in_,
RESP_TO:=_uint_in_,
DONE=>_bool_out,
ERROR=>_bool_out_,
STATUS=>_word_out_,
MB_DB:=_fbtref_inout_);
The MB_COMM_LOAD instruction configures a
PtP port for Modbus RTU protocol
communications. Modbus port hardware options:
Install up to three CMs (RS485 or RS232), plus
one CB (R4845). An instance data block is
assigned automatically when you place the
MB_COMM_LOAD instruction in your program.
Table 12- 64 Data types for the parameters
Parameter and type
Data type
Description
REQ
IN
Bool
A low to high (positive edge) signal starts the operation.
(Version 2.0 only)
PORT
IN
Port
After you install and configure a CM or CB communication device, the
port identifier appears in the parameter helper drop-list available at the
PORT box connection. The assigned CM or CB port value is the device
configuration property "hardware identifier". The port symbolic name is
assigned in the "System constants" tab of the PLC tag table.
BAUD
IN
UDInt
Baud rate selection:
300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 76800, 115200,
all other values are invalid
PARITY
IN
UInt
Parity selection:
0 – None
1 – Odd
2 – Even
FLOW_CTRL
IN
UInt
Flow control selection:
0 – (default) no flow control
1 – Hardware flow control with RTS always ON (does not apply to
RS485 ports)
2 – Hardware flow control with RTS switched
