Compaq 1700 Compaq Armada 1700 Series Reference Guide - Page 80

Using AT Commands to Control the Modem, mode, that is

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Using AT Commands to Control the Modem The internal modem can be used in a variety of applications and is designed to interface with a wide range of computer and data communications equipment. Because each device has specific requirements of its own, the modem is equipped with an extensive set of commands and registers that you can set to meet the specific requirements of your system. The modem always operates in one of two modes: the command mode or the online mode. When power is turned on, the modem automatically assumes the command mode. When the modem is in the command mode, it can be configured for your computer system or for a particular application. You can use your communications software, such as Windows HyperTerminal, to program the modem. In most cases, you can merely select the options and operations required from a menu in the communications software program. The communications program transmits these selections to the modem in the form of commands. The modem then processes the data received as instructions to perform a particular task. However, you can also issue commands directly from the terminal mode of the communications program. Using the AT command set, Class 1 fax extensions, and supporting S registers, you can instruct the modem to perform a particular function or set of functions. For example, you may instruct the modem to dial (ATDn), answer (ATA), and hang up (ATH0) with the appropriate commands. You cannot enter commands when the modem is in the online mode, that is, sending or receiving data over the telephone lines. However, the modem returns to the command mode under the following circumstances: s A call is disconnected, and the modem goes offline. s The modem cannot successfully complete a call, or if the data carrier of the remote modem is dropped. s The modem receives a defined escape sequence or break signal while in the online mode. s A semicolon (;) occurs at the end of a dialing string. If an error occurs during the execution of a command line, processing of the command line stops, and everything following the erroneous command is ignored. 7-10 Using the Internal Modem

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7-10
Using the Internal Modem
Using AT Commands to Control the Modem
The internal modem can be used in a variety of applications and is
designed to interface with a wide range of computer and data
communications equipment. Because each device has specific
requirements of its own, the modem is equipped with an extensive
set of commands and registers that you can set to meet the specific
requirements of your system.
The modem always operates in one of two modes: the command
mode or the online mode. When power is turned on, the modem
automatically assumes the command mode. When the modem is in
the command mode, it can be configured for your computer
system or for a particular application.
You can use your communications software, such as Windows
HyperTerminal, to program the modem. In most cases, you can
merely select the options and operations required from a menu in
the communications software program. The communications
program transmits these selections to the modem in the form of
commands. The modem then processes the data received as
instructions to perform a particular task.
However, you can also issue commands directly from the terminal
mode of the communications program. Using the AT command
set, Class 1 fax extensions, and supporting S registers, you can
instruct the modem to perform a particular function or set of
functions. For example, you may instruct the modem to dial
(ATDn), answer (ATA), and hang up (ATH0) with the appropriate
commands.
You cannot enter commands when the modem is in the online
mode, that is, sending or receiving data over the telephone lines.
However, the modem returns to the command mode under the
following circumstances:
■
A call is disconnected, and the modem goes offline.
■
The modem cannot successfully complete a call, or if the data
carrier of the remote modem is dropped.
■
The modem receives a defined escape sequence or break
signal while in the online mode.
■
A semicolon (;) occurs at the end of a dialing string.
If an error occurs during the execution of a command line,
processing of the command line stops, and everything following
the erroneous command is ignored.