Siemens SIMATIC S7 Manual page 21

Insertion of the
Communication
Blocks
CP 300
CP 400
OPEN MODBUS / TCP communication via CP343-1 and 443-1
2XV9450-1MB00; Manual edition 4.3
The Modbus function blocks use the function blocks AG_SEND and
AG_RECV in S7-300 or AG_LSEND and AG_LRECV in S7-400.
You can find these communication function blocks in the library
"SIMATIC_NET_CP" which are included in the software package NCM S7
for Industrial Ethernet.
Copy the functions FC5 (AG_SEND) and FC6 (AG_RECV) from the folder
"CP 300" and insert in your project.
Copy the functions FC50 (AG_LSEND) and FC60 (AG_LRECV) from the
folder "CP 400" and insert in your project.
Please note, that the following versions of the FCs are a prerequisite for the
faultless function of the FB MODBUSCP:
S7-400: AG_LSEND
AG_LRECV
S7-300: AG_SEND
AG_RECV
V3.1 or higher
V3.1 or higher
V4.2 or higher
V4.7 or higher
Commissioning
3-11