Quantum PLC Programming via modem


Thread Starter

S. Gagnon

I would like to know if its possible to download the program in the Quantum PLC via modem link. The distance between the programming station and the PLC is very important (about 5 km). Its impossible to put the PLC on ENET network on RF. So, i had the idea to put the modem on the PLC Modbus port and the PC COM1 port. When I want to download the program in the PLC, I just open the
connection between both modem (with Hyper terminal) and after that download in the PLC. Is somebody has tried that?

I've tried that on a 984 Modicon PLC before and it worked fine. The PLC's serial port was connected to one modem (in auto-answering mode). Both modems were linked to the standard phone line (voice line with standby tone). Once the comm channel is openned through both modems, use the PLC software as if you were connected directly into the PLC serial port.

Pay attention to PLC and PC baudrate when using PLC software to download programs. It should be less or equal the modem capacity.

Good luck.
What programming software package are you using ? With Proworx NxT, the communication setup lets you select a dialup modem. You will
probably have to have your PLC Modbus port set to ASCII mode for this to work well

I do not see any communication setup for a modem in Concept 2.2.

When I have tried to make Hyperterminal dial a modem for me, it grabs the comm port for itself, when Hyperterminal closes, it hangs up the modem. If there's a way to make that work I'd like to know also.

Jay Kirsch

We do this all the time with our Siemens PLCs. It should be no different with any PLC that has a serial connection.
We do this a lot, and there are a few things that we've found.

The remote modem must always be set to auto answer, and you may have to configure the modem to disable compression, hardware handshaking, etc. We generally use USRobotics Sportser 56k external modems, and sending modem commands AT&F0&W to both modems bdfore installation has worked for us.

You are right in that setting up for ProWorx is pretty seamless, as it has a built-in dialer, and you have to go with ASCII 7E1. Depending on line quality, we've had to dropo down from 19200 to 9600 baud in some locations.

To do this in Concept 2.2, we don't use HyperTerminal, but instead use the Terminal program which was available in Win95. We set up the dialing in Terminal, and you must include &D0 in the initialization string. This tells the modem to ignore the DTR command. Once the connection is made, you can shut down Terminal, and it asks you whether you want to stay connected. Choose staying connected, and if you've configured for &D0 it doesn't hang up the modem. Then you can go online with Concept as if its a normal serial connection.

We've done the same thing for connecting GE-Fanuc Cimplicity software which doesn't have built-in dialing.


Don Zunti, P. Eng.
Delco Automation Canada

Tomy Zacharia

Hi List,
If you have an external modem then it can be programmed or rather a setting can be stored in nv-ram to ignore the DTR signal. So even after
powerdown it will "remember" the setting. I think the dtr signal is used by comms software to indicate that the modem is being controlled by it. The settings can be found by browsing through the AT command list provided by the manufacturer of the modem. good luck.

Tomy Zacharia
Telecom and Instrumentation Engineer.