Siemens S7-1200 System Manual page 740

Communication processor and Modbus TCP
12.5 Modbus communication
Table 12- 61 Example of Modbus holding register addressing
HR_Start_Offset
0
20
HR_Start_Offset is a word value that specifies the starting address of the Modbus holding
register and is stored in the MB_SERVER instance data block. You can set this public static
variable value by using the parameter helper drop-list, after MB_SERVER is placed in your
program.
For example, after MB_SERVER is placed in a LAD network, you can go to a previous
network and assign the HR_Start_Offset value. The value must be assigned prior to
execution of MB_SERVER.
740
Address
Modbus address (Word)
S7-1200 address
Modbus address (Word)
S7-1200 address
Minimum
40001
MW100
40021
MW100
Entering a Modbus server
variable using the default DB name:
1. Set the cursor in the parameter field and
type an m character.
2. Select "MB_SERVER_DB" from the drop-
list of DB names.
3. Select
"MB_SERVER_DB.HR_Start_Offset" from
the drop-list of DB variables.
System Manual, 03/2014, A5E02486680-AG
Maximum
40099
MW298
40119
MW298
S7-1200 Programmable controller