Siemens SIMATIC S7-1200

Communication processor and Modbus TCP
13.8 Legacy Modbus TCP communication
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
1249
13.8
Legacy Modbus TCP communication
13.8.1
Overview
Prior to the release of STEP 7 V13 SP1 and the S7-1200 V4.1 CPUs, the Modbus TCP
communication instructions existed with different names, and in some cases, slightly
different interfaces. The general concepts apply to both sets of instructions. Refer to the
individual legacy Modbus TCP instructions for programming information.
13.8.2
Selecting the version of the Modbus TCP instructions
There are three versions of the Modbus TCP instructions available in STEP 7:
● Legacy version 3.0: Compatible with all CPU and CP versions
● Legacy version 3.1: Compatible with all CPU and CP versions
● Version 4.1: Compatible with V4.0 and later CPUs and V2.1 and later CMs
For compatibility and ease of migration, you can choose which instruction version to insert
into your user program.
Do not use both 3.0 and 3.1 instruction versions in the same CPU program. Your program's
Modbus TCP instructions must have the same major version number (
1
.x,
2
.y, or
V
.z). The
individual instructions within a major version group may have different minor versions (1.
x
).
Click the icon on the instruction tree task card to enable the headers and columns
of the instruction tree.
To change the version of the Modbus TCP
instructions, select the version from the drop-
down list. Y
ou can select the group or indi-
vidual instructions.
When you use the instruction tree to place a Modbus TCP instruction in your program, a new
FB instance is created in the project tree. You can see new FB instance in the project tree
under PLC_x > Program blocks > System blocks > Program resources.
To verify the version of a Modbus TCP instruction in a program, you must inspect project
tree properties and not the properties of a box displayed in the program editor. Select a
project tree Modbus TCP FB instance, right-click, select "Properties", and select the
"Information" page to see the Modbus TCP instruction version number.