Friday, January 21, 2011

The Connection PLC and PLC_DIAL over Telephone Line

The PLC_DIAL is a Window 32 bit application program which allows connecting running on the computer Serial DDE Server and PLC (Programmable Logic Controller) over the telephone line, so making available the data exchange between PLC and DDE Server.

The connection between PLC and PLC_DIAL can be opened in two following ways: by calling from PLC_DIAL to PLC or by receiving a call from PLC in PLC_DIAL. Secondly case the modem used by PLC_DIAL must be configured to automatic answering mode.

To connect PLC and Serial DDE over the telephone line you need 2 modems, one at each side. Firstly, you must configure the Remote Modem, the Modem used at PLC side (the Remote Modem configuration may be not needed if the PLC can call to PLC_DIAL, e.g. PLC_DIAL is used in a ”waiting for a call” mode). This modem must be able to save its configuration to its non volatile memory. Modem used at Serial DDE Server (computer) side, local modem may not have this feature. You must configure Remote Modem only once, when it is configured it must be connected to PLC and telephone line.

The next step is to configuring the Local Modem. When local modem is ready then connection between PLC and PLC_DIAL can be established. This step is needed every time you want to start the Serial DDE Server. The connection can be opened by calling from PLC to PLC_DIAL or by receiving a call from PLC in PLC_DIAL. After the connection is established, you have to close the communication port used by local modem, without hanging up the modem, and start the DDE Server. You can start the DDE Server directly from the PLC_DIAL. When the DDE Server is started can close the PLC_DIAL.
After you close the DDE Server you must hang up modem. You can do it manually in PLC_DIAL, by DDE from application client or simply by switching off the modem power.

The PLC_DIAL can be started with two commands in line parameters. One parameter is the phone number to dial when PLC_DIAL is started. The second parameter is the name of executable to be started after dialing.

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