Siemens SIMATIC ET 200SP Function Manual

Open User Communication
6.7 Setting up communication with Modbus TCP
Communication
86 Function Manual, 11/2019, A5E03735815-AH
Modbus TCP server as gateway to Modbus RTU
If you use a Modbus TCP server as a gateway to a Modbus RTU protocol, address the slave
device in the serial network using the static parameter, MB_UNIT_ID. The MB_UNIT_ID
parameter corresponds to the field of the slave address in the Modbus RTU protocol. The
MB_UNIT_ID parameter in this case would forward the request to the correct Modbus RTU
slave address.
You do not have to program the gateway function yourself.
You can find the MB_UNIT_ID parameter in the instance data block associated with
MB_CLIENT instruction.
You can find more information on the MB_UNIT_ID parameter in the STEP 7 online help.
Reference
● This FAQ (https://support.industry.siemens.com/cs/ww/en/view/94766380) describes how
to program and configure the Modbus TCP communication between two S7-1500 CPUs.
● This FAQ (https://support.industry.siemens.com/cs/ww/en/view/102020340) describes
how to program and configure Modbus TCP communication between an S7-1500 CPU
and an S7-1200 CPU.

Siemens SIMATIC ET 200SP Specifications

General

System Type	Distributed I/O System
Mounting	DIN Rail
Communication Protocol	PROFINET, PROFIBUS
IP Rating	IP20
Category	I/O Systems
Supply Voltage	24 V DC
Modularity	Yes
Hot Swapping	Yes
Storage Temperature	-40°C to +70°C
Digital Inputs	Yes
Digital Outputs	Yes
Analog Inputs	Yes
Analog Outputs	Yes
Communication Interface	PROFINET, PROFIBUS
Number of Modules	Up to 64
Relative Humidity	5 to 95% (non-condensing)
Operating Temperature	-25°C to +60°C