Example configurations for modems at the I/O Server

The examples below demonstrate how to set up the modems at your I/O Server to accommodate different combinations of I/O Devices.

Example 1

All your remote I/O Devices have the same communication requirements (data bitsGroup of binary digits (bits) used to represent a single character of data in asynchronous transmission., stop bitsThe number of bits that signals the end of a character in asynchronous transmission. The number is usually 1 or 2. Stop bits are required in asynchronous transmissions because the irregular time gaps between transmitted characters makes it impossible for the server or I/O device to determine when the next character should arrive., parityA communications error-checking procedure. The number of 1's must be the same (even or odd) for each group of bits transmitted without error., and baud rateThe number of times per second a signal changes in a communication channel. While the baud rate directly affects the speed of data transmission, the term is often erroneously used to describe the data transfer rate. The correct measure for the data rate is bits per second (bps).) - 19200 8 E 1.

You don't expect any important calls from your I/O Devices, or you only have a few remote I/O Devices. This means you can use a single modem at the I/O Server end. This modem would be set up to answer and return incoming calls and make scheduled and other CitectSCADA initiated calls.

To configure your modem, define it in Windows. Assuming that the logical modem is called 'Standard Modem', configure it as follows:

You would then configure it in CitectSCADA as a dial-out modemMakes calls to remote I/O devices in response to a request; e.g., scheduled, event-based, operator request, and so on. Also returns calls from remote I/O devices. and dial-in modemOnly receives calls from remote I/O devices, identifies the caller, then hangs up immediately so it can receive other calls. then returns the call using a dial-back modem.:

Example 2

In this example, your I/O Devices use a total of two different communication specifications - 9600 7 O 1 and 19200 8 E 1.

You don't expect important calls from I/O Devices or you have only a few I/O Devices. This means you can get by with a single modem at the I/O Server end. This modem has to receive and return calls from I/O Devices as well as initiate calls (dial out) to I/O Devices.

To configure your modem, you need to first define it in Windows (through the Windows Control Panel). Remember, you're not just defining the physical modem here. You have to define a separate Windows (virtual) modem for each communication specification.

So far, this gives you two virtual modems - one for 9600 7 O 1 and one for 19200 8 E 1. However, Windows won't let you define both of these modems as dial-in. It only lets you define one dial-in modem per port. If you choose the first, it won't be able to receive calls with the second, and vice versa.

This means you have to set up a separate virtual modem that can answer calls no matter which communication specification is used. This modem would be set with a generic communication specification of 9600 8 N 1.

So in Windows, you'll end up with three logical modems (two for Dial-Out and one for Dial-In). Assuming that the logical modems are called 'Standard Modem' to 'Standard Modem #3', you would configure them as follows:

You would then configure the modems in CitectSCADA as follows.

Example 3

In this example, there are five different communications frameworks - 9600 7 O 1, 19200 8 E 1, 4800 8 N 1, 9600 8 N 1, and 19200 8 N 1.

If you expect important calls from I/O Devices or you have many I/O Devices, you would set up three modems at the I/O Server end:

• One on COM3 dedicated to receiving calls from 9600 7 O 1 I/O Devices.
• One on COM2 for dialing out to 4800 8 N 1, 9600 8 N 1, and 19200 8 N 1 I/O Devices.
• One on COM1 for dialing out to 9600 7 O 1 and 19200 8 E 1 I/O Devices.

The two dial-out modems would return calls as well as initiate calls in response to scheduled requests, and so on.

To configure your modems, you need to first define them in Windows (through the Windows Control Panel). Remember, you're not just defining the physical modem here. You have to define a separate Windows (virtual) modem for each communication framework.

Assuming that the logical modems are called 'Standard Modem' to 'Standard Modem #6', you would configure them as follows:

You would then configure the modems in CitectSCADA as follows:

Example 4

In this example, your I/O Devices use three different communication frameworks: 9600 7 O 1, 19200 8 E 1, and 9600 8 N 1. However, in this example, you are expecting important calls from I/O Devices, so you need a modem dedicated to returning calls.

Here you need to configure your modems like this:

• One modem on COM1 to dial remote I/O Devices (for scheduled calls, and so on).
• One modem on COM2 to receive calls from remote I/O Devices.
• One dedicated modem on COM3 to return these calls.

To configure your modems, first define them in Windows (through the Windows Control Panel). Remember, you're not just defining the physical modem here: you need to define a separate Windows (virtual) modem for each communication framework. This means you have to configure:

• Three logical modems on the port to which the physical dial-out modemMakes calls to remote I/O devices in response to a request; e.g., scheduled, event-based, operator request, and so on. Also returns calls from remote I/O devices. is attached.
• One logical modem on the port to which the physical dial-in modemOnly receives calls from remote I/O devices, identifies the caller, then hangs up immediately so it can receive other calls. then returns the call using a dial-back modem. is attached.
• Three logical modems on the port to which the physical dial-back modemOnly returns calls from remote I/O devices. is attached.

Assuming that the necessary total of seven logical modems are called 'Standard Modem' through to 'Standard Modem #7', configure these modems as follows:

You would then configure the modems in CitectSCADA as follows: