Siemens SIMATIC S7-1200 - Page 1259

Communication processor and Modbus TCP
13.8 Legacy Modbus TCP communication
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
1259
Incoming Modbus message function codes function codes (3, 6, and 16) read or write words
in a Modbus holding register which can be an M memory address range or a data block. The
type of holding register is specified by the MB_HOLD_REG parameter.
Note
MB_HOLD_REG parameter assignment
The Modbus Holding Register can be in a non
-optimized global DB or an M memory
address.
For A Modbus holding register in M memory, use the standard Any Pointer
format. This is in
the format P#"Bit Address" "Data Type" "Length". An example would be P#M1000.0 WORD
500
The following table shows examples of Modbus address to holding register mapping used for
Modbus function codes 03 (read words), 06 (write word), and 16 (write words). The actual
upper limit of DB addresses is determined by the maximum work memory limit and M
memory limit, for each CPU model.
Table 13- 138 Mapping examples of Modbus address to CPU memory address
Modbus Address
MB_HOLD_REG parameter examples
P#M100.0 Word 5
P#DB10.DBx0.0 Word 5
"Recipe".ingredient
40001
MW100
DB10.DBW0
"Recipe".ingredient[1]
40002
MW102
DB10.DBW2
"Recipe".ingredient[2]
40003
MW104
DB10.DBW4
"Recipe".ingredient[3]
40004
MW106
DB10.DBW6
"Recipe".ingredient[4]
40005
MW108
DB10.DBW8
"Recipe".ingredient[5]