Almost all modems today support AT commands. With this protocol, a command to the modem to initiate an action or a setting change is prefixed with the letters "at", usually, but not always, case-insensitive. Typing a line of text to the modem followed by a carriage return (CR, the ENTER key) will have no effect and receive no response unless it starts with "at" (for attention).

The modem will respond to a command entry with "OK" if it is recognised, or with "ERROR" if an unrecognised command is typed.

Although WTC can be set up to work with other situations, it is unlikely that you will encounter a modem that does not support the AT command protocol in most circumstances, and we discuss modem setup in this context.

The most basic AT "command" is "at" itself, which just produces an OK response. This can be used to verify that a connection to a modem is live. AT commands can be stringed together without repeating the "at", which only needs to be there once at the beginning of the line. There is usually no requirement for spacing between consecutive settings on the same line, the modem ignores white space, but spacing can improve clarity for some. Modems usually ignore the case of command characters too, though some may not, try all uppercase if the modem gives an error response to an apparently valid command.

The interactive terminal configuration of WTC allows you to communicate with the modem in command mode, typing in AT commands and reading the response on screen. Feedback from the dialling and answer commands is displayed as well. Normally, when you select a number to dial or answer a cal, the modem's response to the command is captured by Windows Text Communications and not displayed, which makes for neater day-to-day operation. The interactive terminal, however, allows all modem feedback to be displayed, so that you can verify what is actually being sent when you try to dial or answer.

In addition, the interactive terminal configuration verifies the modem initialisation string in a dialogue box. It is possible that the modem does not echo characters during initialisation, in which case the intended transmission would not be verifiable. If modem initialisation is enabled, WTC displays a message box confirming the string that was sent out when the transmission is complete. You may need to consult your modem manual to find out how to set it to echo characters back at all, although this is usually part of the modem's default settings, which initialisation strings should always start by resetting using "AT&F" or "AT&F0", before making specific changes. If the modem does not echo back, you can switch WTC's local echo on from the communications settings menu or by including it in the interactive terminal shortcut command line with the "p,,,,,h,,0" directive. However, WTC's local echo will only provide feedback to typing, but there can be no verification of auto-executed commands. If command verification is required, you need to enable modem echo. The command:

"ATE1"

is worth trying to enable modem echo-backs, if this fails, consul the modem documentation.

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AT Commands