Communicating with Remote Devices via Modems

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Communicating with Remote Devices via Modems

A dial-up remote I/O device is one which is connected to Citect SCADA through a PSTN (Public Switched Telephone Network), and is accessible through pre-selected and pre-configured modems. Once connected, Citect SCADA can write to, and read from, dial-up remote I/O devices just as it does with any other local or remote I/O device.

Communications can be:

On request: initiated by Citect SCADA using IODeviceControl() or by the remote I/O device (for instance, to report an alarm condition).
Periodic: for instance, to transfer the logged events for a period.
Persistent: for instance, to monitor and control the water level at a remote dam.

The only limiting factor would be an inability to connect a modem to an I/O device due to incompatible communications capabilities. Many I/O devices have fixed settings and can only communicate at a pre-set rate determined by the manufacturer. If a modem cannot match these settings, communication cannot be established.

To make communications setup easier, you can connect dial-up remote I/O devices with identical communications to the same modem and port. Where I/O devices are connected to the same modem, Citect SCADA can communicate with each I/O device one after the other using the same phone connection, rather than hanging up and re-dialing. This reduces the number of necessary telephone calls and increases the speed and efficiency of communications.