Multi-Tech Systems BA-Series manual AT Command Editing, Functional Modes

MultiModemBA User Guide

4.1Introduction

AT commands are the means by which you, and your communications software, are able to communicate with and configure your modem. They enable you to establish, read, and modify parameters in addition to dialing. The following provides both a summary and a detailed explanation of the AT commands recognized by the MultiModem.

4.1.1AT Command Editing

The BACKSPACE key on your keyboard can be used to edit characters in the AT command line. An AT command is not executed until the RETURN key is pressed. The BACKSPACE key erases the previous character for reentering.

The BACKSPACE key does not erase the AT characters once they are entered. If your keyboard has no BACKSPACE key, CTRL-Hdoes the same thing. The character recognized by the modem as BACKSPACE may be changed to any other ASCII character with S-Register S5.

If you wish to cancel an entire command that has been entered but not yet executed, enter CTRL-X. This also clears the command buffer. The effect is the same as backspacing to cancel the entire command, only quicker.

Characters entered in a command are stored in the modem's Command Buffer (memory) until executed by hitting RETURN. The Command Buffer's capacity is sixty characters. The Attention Characters AT do not count in the sixty allowed Command characters. Spaces, which may be used for increased display readability, may be used when entering a command, but are not stored in the Command Buffer and are not counted in the sixty allowed characters. Hyphens, parentheses, etc. are not allowed.

If the sixty character limit is exceeded or if invalid characters are entered, the Command Buffer automatically erases, and an ERROR message appears. You would then re-enter your command within the sixty-character maximum, using only the allowed characters.

4.1.2Functional Modes

The MultiModem can be in one of two functional states (see Figure 4-1). These are "Command mode" and "On-line mode". (There is also an in-between state, "Wait-for-Carrier", where the modem is out of Command mode but not yet really On-Line.

When the modem is initially powered up, it is in Command mode and is ready to accept commands from your keyboard or software. The modem enters On-line mode after dialing, making a connection with another modem, and then detecting a valid carrier signal. If no carrier is detected within a certain time frame, the modem abandons the call and re-enters Command mode.

Once on line, the modem exits On-line mode if one of two conditions is met. If the carrier is lost or intentionally dropped, the modem hangs up and re-enters Command mode. Also, if the modem recognizes the Escape sequence for which it is configured (i.e., either the Escape characters in the serial data stream, the Remote Escape characters in the modulated data stream, or the Break signal), the modem will exit On-line mode, retain the datacomm link, and enter Command mode.

You can force the modem into On-line mode without dialing by sending the ATD or ATA command to the modem.

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