Multi-Tech Systems ISIHP-4U, ISIHP-4SD manual Command Structure, Command Editing

Modem AT Commands & S-Registers

mode without losing the carrier signal. While waiting to establish the carrier, you can type any character from the keyboard to make the modem to go back to the command mode.

Command Structure

You can control a wide variety of modem operations and options when the modem is in command mode. AT commands tell the modem to dial a number, to answer a call, to operate at a certain speed, to use a certain compression technique, and many other functions. AT commands consist of one or two letters, which may be preceded by an ampersand (&), a percent character (%), or a slash character (/). The Q command, for example, determines whether the modem returns result codes, while the &Q command selects the asynchronous communications mode.

A parameter after a command (0, 1, 2, etc.) tells the modem which option to use. If you do not specify a parameter, the modem assumes the 0 (zero) option. E, for example, is the same as E0. You can issue several commands on a single line (a command string) as long as the line does not exceed 40 characters.

Note: Each character in a command counts toward the 40 character

command line maximum. Example: Q1 is a single command, but it counts as two characters in the command line.

Each command has a valid range of parameters. For example, &S can have only 0 or 1 as a parameter. Valid commands always generate an OK result code, and a few generate an additional response such as a list of parameters. An invalid command such as &S3, which has a parameter outside the valid range, generates an ERROR result code. Most commands have a default parameter that is enabled when the modem is turned on or reset with the ATZ or AT&F command. Factory defaults are stored in read-only memory (ROM) and cannot be changed. User-defined defaults can be stored in nonvolatile random-access memory (NVRAM) and can be changed or deleted at will.

Command Editing

Always begin a command with the letters AT. Enter the entire command string in upper or lower case, but do not mix cases within the command

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