Modem for Siemens S7-200 PLCs?

Is there a modem available to establish remote communication with two siemens S7-200 (CPU 224XP) PLC? I know Siemens has a modem module available but with that it seems as though I would need one modem module for each processor. I am wondering if there is any third party modem that could communicate with two CPUs?

The main purpose of remote communication would be to download/monitor the PLC program.. Is this possible?

Hi Cryogen, don't know if this is applicable or relevant, but you could use a couple of GSM or GPRS modems. Siemens make their own or any other will work (Westermo, Sixnet etc) - we can pick up a Siemens GSM for about £100 (TC35i or MC35??). Then just hang it off one of the 224XP com ports set to freeport mode. You can then output your AT commands (say) straight to the port as String variables using ASCII.

The only issue may be the Rs232 to RS485 connection - i know you can lash up a lead and a resistor (got a diagram somewhere?), otherwise you may need a converter......

Hope this helps!

Hi Cryogen,

Any cheap modem would do the job. If your need is to download/monitor use any modem.
I am using the Trendnet TFM-560X modem which is around 30 USD
to support projects overseas without any problem.

Hello Cryogen;

it seems as though I would need one modem module for each processor.

Click to expand...

Of course you will need one modem for each s7-200 CPU, and one on the PC you plan to use to monitor/download (e.g. running MicroWin).

Hope this helps,
Daniel Chartier

PPI communication trough modems between Microwin(local) and PLC(remote) isn`t
the same as PLC to PLC communication.

Microwin accepts larger timeouts, beacuse it is the Master(initiator) in this communication.

A communication request initiated by a PLC trough NETR/NETW has a fixed timeout value, which is designed for a local communication (low distance -> small delays).

The possibility of PPI communication trough remote connections generally depends on:


phone line delay (e.g. bad intercontinental connetions with large delays(gaps))
<LI>modem delay (caused trough internal conversion, buffering)

Workaround:

1. Take a EM241 modem module on each side (master and slave). EM241 supports fixed
lines only.
(Any side could initiate the communication in this constellation, so master and slave
could change during runtime)

2. Take a EM241(master) and a GSM-TC35(slave) + PC/PPI cable(6ES7 901-3CB30-0XA0) in
multimaster mode (not tested, tip from a 3rd party)
(Only the EM241 could initiate a communication in this way)

3. Use two regular modems + 2x PC/PPI cable (older cable works too). In this case you
must use freeport communication.
You should take therefore modbus or implement a another small protocol. You will find
the modbus master library on www.s7-200.net, the modbus slave you get with oderno.
(6ES7 830-2BC00-0YX0) for about 99EUR/USD.
The modbus libraries has a adjustable timeout parameter.
Depend on configuration only one (or any) side could initiate the communication

Thanks for all your replies..
I already have a cable running for PLC-PLC communications. I am using the NETR/NETW to transfer data. Separately I want to have ability to load programs on both the PLCs.

Is the GSM for connection to the PC(MicroWin)?
So from my understanding, one of the possibilities:

PC --> GSM ========= EM241 --> PLC?

== Phone line

Is this correct or have I completely mistaken?