Sierra Wireless DART 200 CDPD Modem Escape sequence considerations, Command response options

DART 200 CDPD Modem User’s Guide 8 Application Programming

CAUTION:

Do not reduce the guard time to zero, because this exposes the application to an unwanted escape if three successive escape characters inadvertently appear in the data stream. Leave the guard time as larger than the expected inter-character time in the MAS to modem data transfer. Each unit of guard time is approximately 20 milliseconds.

Escape sequence considerations

The escape sequence is one of two ways the MAS forces the DART 200 to leave online or SLIP mode and return to command mode. The other is to drop the DTR line, as described in Escaping through the control interface, p. 8-16.

Leaving online or SLIP mode is required for the DART 200 to respond to AT commands. Commonly, this occurs at the completion of a session to terminate the connection (hang up) with the ATHn command. Another common reason is to interrogate modem status for local radio resource conditions, or for error recovery operations.

The DART 200 escape sequence consists of three escape characters (E) and a 1-second guard time (G). Unlike standard Hayes-compatible modems that use a GEEEG escape sequence, the DART 200 uses an EGEGE sequence. Whether or not the escape characters are passed onto the network as data (&E1) or filtered from the output data stream (&E2) can be specified.

Escape code recognition controls whether or not the DART 200 responds to the escape code. The default is &E1 (recognition enabled and the escape sequence is passed to the network). For manual operation this feature must be enabled (&E1 or &E2). For application use it can be disabled (&E0) if the MAS can control the DTR lead in the RS-232 interface. However; even in this case, the &E0 option is not recommended as the inability to escape manually it can limit debugging capability.

The escape character (+) is in S-Register 2 and the guard time (50 in units of 1/50 second) is in S-Register 12: both can be changed at set up time or under application control. There is no obvious reason to change the escape character, but it can be desirable in interactive applications to reduce the guard time from its 1-second default value to improve application responsiveness.

?

NOTE:

Terse mode only applies to command responses (such as AT). Register or modem status inquiries (such as ATS57?) will still provide a response which is bracketed by both carriage return <CR> and linefeed <LF> characters.

Command response options

There are three setup options controlling if, and how result codes are presented to the MAS:

∙Quiet Mode (Qn) - Controls whether or not result codes are returned to the MAS. The default value is enabled (Q0). There are few situations where an application can operate without seeing return codes. However, some non-intelligent devices can be attached to the DART 200, that do not expect anything but poll characters; in that situation Quiet Mode enabled (Q1) is appropriate. Use the default (Q0) except in these special situations

Sierra Wireless, Inc. 8-20