Serial Programming/Modems and AT Commands/Special Commands and Character Sequences

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Serial Programming: Introduction and OSI Network Model -- RS-232 Wiring and Connections -- Typical RS232 Hardware Configuration -- 8250 UART -- DOS -- MAX232 Driver/Receiver Family -- TAPI Communications In Windows -- Linux and Unix -- Java -- Hayes-compatible Modems and AT Commands -- Universal Serial Bus (USB) -- Forming Data Packets -- Error Correction Methods -- Two Way Communication -- Packet Recovery Methods -- Serial Data Networks -- Practical Application Development -- IP Over Serial Connections

Hayes-compatable Modems and AT Commands References: -- Special AT Commands and Character Sequences -- AT Commands A - M -- AT Commands N - Z -- AT& Commands

Special Commands and Character Sequences[edit]

This module explains the special commands and character sequences as used by a "generic" Hayes-compatible modem. Different modems use slightly different commands. However, this list is supposed to be as "generic" as possible, and should not be extended with modem-specific commands. Instead it is recommended to provide such command lists in an Appendix.

AT: Command Prefix[edit]

Syntax:

AT<command ...><CR>

Description:

Almost every line with commands start with the AT prefix, followed by one or more commands, terminated with a Carriage Return character.

See the #AT Command Format section for details.

Related Commands and Registers:

+++: Escape Sequence[edit]

Syntax:

<1 sec. nothing>+++<1sec. nothing>

Description:

See: #On-line State to Command State

Result Codes:

Result Codes
Code Description
OK Escape into command mode was successful

Related Commands and Registers:

<CR>: End-of-line Character[edit]

Syntax:

AT command line<CR>

Description:

In command mode the end of line character (default ASCII 13, alias ASCII 0dH, alias <CR>, alias <Ctrl-M>, alias carriage return) marks the end of a command line. The modem starts to execute the command line after reception of the end-of-line character.

Result Codes:

Result Codes
Code Description
OK All commands in the command line were successfully executed.
ERROR One command in the command line failed.

Related Commands and Registers:

<BS>: Backspace Character[edit]

Syntax:

AT command line<BS>more command line

Description:

In command mode the backspace character (default ASCII 8, alias ASCII 08H, alias <BS>, alias <Ctrl-H>, alias backspace) can be used to edit the command line.

Result Codes:

Result Codes
Code Description
<none> Does not generate a result code.

Related Commands and Registers:

<CAN>: Cancel Character[edit]

Syntax:

AT command line<CAN>

Description:

In command mode the cancel character (default ASCII 24, aka ASCII 18H, aka <CAN>, aka <Ctrl-X>) cancels a command line as long as the command line has not been terminated with the #<CR>: End-of-line Character.

Result Codes:

Result Codes
Code Description
<none> No result code is returned.

Related Commands and Registers:

A/: Repeat Last Command[edit]

Syntax:

A/

Description:

The command repeats the last command. It differs from other commands in two ways:

  1. It is not prefixed with the AT command.
  2. It should not be followed by the usual <CR>:

The most typical usage is to repeat a previous dialing command that failed because of a BUSY line.

Related Commands and Registers:

Serial Programming: Introduction and OSI Network Model -- RS-232 Wiring and Connections -- Typical RS232 Hardware Configuration -- 8250 UART -- DOS -- MAX232 Driver/Receiver Family -- TAPI Communications In Windows -- Linux and Unix -- Java -- Hayes-compatible Modems and AT Commands -- Universal Serial Bus (USB) -- Forming Data Packets -- Error Correction Methods -- Two Way Communication -- Packet Recovery Methods -- Serial Data Networks -- Practical Application Development -- IP Over Serial Connections

Hayes-compatable Modems and AT Commands References: -- Special AT Commands and Character Sequences -- AT Commands A - M -- AT Commands N - Z -- AT& Commands