Digicom 3910, 3911 operation manual AT Command Set and S-Registers14, Operating Modes

AT Command Set and S-Registers14

Overview

The AT command set provides an alternative method to the modem’s DCP for entering commands that control the operation and configuration of the 391x Series modems. This chapter discusses guidelines necessary to operate AT commands as well as listing the modifiers for all AT commands supported by the 391x Series modems. AT commands are issued from asynchronous DTEs.

Operating Modes

The 391x Series modem has two operating modes, Command mode and Data mode. Before a modem goes online (establishes a successful connection with a remote modem), it is considered to be in Command mode; an idle state where you can modify its operating parameters or issue modem commands. (Any command issued is acknowledged with a response in either words or digits known as Result Codes. Refer to Table 14-1 for a listing of result codes.)

Once the modems are online, either by answering or originating a call, they automatically switch to Data mode. Data mode is a state where any entries made from the DTE are considered data and are transmitted and received between modems. The modems remain in Data mode until the connection is broken or until they are forced into online Command mode using the escape sequence.

Switching Between Data Mode and Online Command Mode

Sometimes it is necessary to change operating parameters while the modems are online. The Escape Sequence allows you to toggle the modem between Data mode and online Command mode while maintaining a connection with the remote modem. This is accomplished using the escape sequence ( + + + ) to exit Data mode and the O command to return to Data mode.

Escape Sequence and Escape Guard Time

The escape sequence is only issued when the modem is online and in Data mode. The 391x Series modem uses three consecutive plus ( + ) characters as the escape sequence. (To change this value, refer to S-Register S2 discussed in Table 14-3 in the S-Register Format section.)

To prevent the modem from interpreting an embedded + + + in data as an escape sequence, the Escape Guard Time value determines the length of the pause before and after the escape sequence is issued. The 391x Series modem uses a one-second pause as the Escape Guard Time. (To change this value, refer to S-Register S12 discussed in Table 14-3 in the S-Register Format section.)

To enter online Command mode while in Data mode, enter the following sequence:

TYPE: + + +

3910-A2-GN32-40 September 1998 14-1