Siemens SIMATIC S7-1200 - Page 1273

Communication processor and Modbus TCP
13.9 Legacy Modbus RTU communication (CM/CB 1241 only)
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
1273
Table 13- 148 Data types for the parameters
Parameter and type
Data type
Description
REQ IN Bool 0=No request
1= Request to transmit data to Modbus slave
MB_ADDR IN V1.0: USInt
V2.0: UInt
Modbus RTU station address:
Standard addressing range (1 to 247)
Extended addressing range (1 to 65535)
The value of 0 is reserved for broadcasting a message to all Modbus
slaves. Modbus function codes 05, 06, 15 and 16 are the only function
codes supported for broadcast.
MODE IN USInt Mode Selection: Specifies the type of request (read, write, or diagnostic).
See the Modbus functions table below for details.
DATA_ADDR IN UDInt
Starting Address in the slave: Specifies the starting address of the data to
be accessed in the Modbus slave. See the Modbus functions table below
for valid addresses.
DATA_LEN IN UInt Data Length: Specifies the number of bits or words to be accessed in this
request. See the Modbus functions table below for valid lengths.
DATA_PTR IN Variant Data Pointer: Points to the M or DB address (non-optimized DB type) for
the data being written or read.
DONE OUT Bool
The DONE bit is TRUE for one scan, after the last request was completed
with no error.
BUSY OUT Bool
• 0 – No MB_MASTER operation in progress
• 1 – MB_MASTER operation in progress
ERROR OUT Bool The ERROR bit is TRUE for one scan, after the last request was termi-
nated with an error. The error code value at the STATUS parameter is
valid only during the single scan where ERROR = TRUE.
STATUS
OUT
Word
Execution condition code