Synchronous Mode And V.80 At Commands; At Command Set; Data And General Commands - US Robotics 56K USB Modem User Manual

Synchronous Mode and V.80 AT Commands

USRobotics' controller-based modem AT command set supports synchronous command mode and most
of the commands defined in ITU-T Recommendation V.80, which defines in-band modem control and
synchronous data modes for asynchronous host systems. Recommendation V.80 addresses two types of
commands:
• AT commands issued in command mode.
• In-band commands transmitted in the data stream.
The in-band commands are delimited by the hexadecimal characters EM (or numerically, 19h). The
USRobotics controller-based commands set supports the most common AT commands identified in
Recommendation V.80:
• +ES.
• +ESA.
• +IFC.

AT Command Set

AT commands are issued to the modem to control the modem's operation and software configuration. AT
commands can only be entered while the modem is in command mode. The basic command syntax is as
follows:
• <command><parameter>.
The <command> is a combination of the attention prefix (AT) followed by the AT command. The
<parameter> is a string that represents a numeric decimal value.
Any command issued is acknowledged with a response in either text or numeric values. These responses
are known as result codes. The result codes are listed in Result Code Summary on page 107.
Commands may be executed while in command mode, which is entered under one of the following
conditions:
• After powerup, at the termination of a connection, or after the execution of a command other than dial
or answer.
• Upon the receipt of the escape sequence (three consecutive character matching the contents of
resister S2) while in online mode.
• Upon the on-to-off transition of DTR if &D1, &D2, or &D3 has been set.

Data and General Commands

+++ Escape Sequence
An escape sequence allows the modem to exit data mode and enter online command mode. While in
online
command mode, AT commands are sent directly to the modem.
Use the return to online data mode command (O<value>—Return to Online Data Mode on page 18) to
return to data mode.
Place a pause before and after the escape sequence to prevent the modem from interpreting the escape
sequence as data. The length of the pause is set by register S12 (S12—Escape Guard Time on page 99).
The escape guard time. Register S2 (S2—Escape Character (User Defined) on page 97) identifies the
56K USB Modem
User Guide
Command Reference - 11