ModbusTCP for Siemens Simatic S7300


Thread Starter

Roberto Lizano

I have to basic questions:
Besides the send/receive commands sent through the Ethernet conection between two S7-300 PLCs using the CPs 343-1, which other protocols the CPs use to interconnect the PLCs? This, due to the fact that we are interested in knowing if these CPs are able to "speak" any open source protocol; such as Modbus, lets say: installing a driver or in any other way, software or hardware.

On the other hand, we would also like to know if there exists in your products, a solution such as an Ethernet to Modbus bridge, and viceversa, so that we can have a Modbus TCP/IP network ?

Fernando Capelari - Schneider Brazil

Dear friend,

I can not answer your first question about the CP343-1 module, but about your second question, you asked about a solution to bridge an Ethernet to a Modbus network.

Yes, Schneider has that kind of device. The part number is 174CEV30010.

You can download a brochure of that bridge at, clicking in Networks / Ethernet and then Product Information / Publications.

Fernando Capelari
Schneider Electric Brazil

Hakan Ozevin

S7-300 PLC's have connection to Profibus directly from the CPU (...-DP versions) or from a CP. In the near future, Ethernet connection will be integrated to the CPU's as a standard.
Also, using CP341 and loadable drivers, S7-300 PLC's can be connected to almost every system, including Modbus. With the cheap version of this module, CP340, you can also write your own drivers for any protocol based on TTY, RS232 or RS485 hardware.

david mertens

The CP343-1 is an ethernet CP and as such only uses the ISO, ISO on TCP and TCP/IP protocols to communicate. Siemens also offers CP's for communication with profibus (CP342-5). Two special programmable CP's (CP340 and CP341) are available with optional modules for most serial networks and loadable protocols, including modbus master and modbus slave. (This is not modbus on TCP, but the good old serial modbus). Also RK512, R3694, ASCII, RS232 etc. As far as I know, siemens doesn't have modbus to TCP bridges, nor any other modbus periferials, they only offer the possibility to interface the S7 with existing systems via classic modbus, both as a master or as a slave.