Sierra Wireless DART 200 CDPD Modem - Manual (Page 97)

DART 200 CDPD Modem User’s Guide 8 Application Programming
PN1197-00 Revision 1.0 8-3
4. For a modem functioning as a server, (answering calls or being
polled) activate the appropriate server, TCP (with AT*A1) or UDP
(with AT*A2). The connection can be established automatically by
having auto answer active (S-Register 0 =1), or manually by issuing
an ATA command when the RING message occurs, as described in
Auto Answer setup, p. 8-11.
For both client and server systems, successful completion of the Dial
command (ATD) is indicated by a CONNECT message (verbose mode)
or a 1 (terse mode). This puts the modem in online mode. In this state,
AT commands are ignored, the autobaud function is suppressed, and
flow control (if specified) is enabled.
Data transfer
To accomplish data transfer, the DART 200 must be in online mode.
Data transfer is performed by the Mobile Application Subsystem (MAS)
by sending data to or reading data from the DART 200’s RS-232 serial
port. Unlike the previous activities, data transfer uses device-specific
rather than AT commands. For a PC the I/O commands are directed to
the serial port and use the serial port I/O driver supplied by the operating
system being used.
Outgoing data accumulates in the DART 200 until a data forwarding
condition is reached. The DART 200 then attaches the appropriate
header information, and sends the data onto the CDPD network for
forwarding through the appropriate routers to the target IP Address and
port. Refer to Data forwarding, p. 8-8, for more details.
The incoming packet is received by the DART 200, and the header is
removed, and the data passed, subject to flow control considerations, as
described on p. 8-12, to the attached device.
Modes of operation
A major difference between a Cellular Digital Packet Data (CDPD)
Hayes-compatible network session and a typical synchronous
communications session is the two modes of operation: command mode
and online (data) mode.
AT commands are issued and responded to by the DART 200 when in
command mode. Once a remote station is dialed, or SLIP mode is
started, the modem enters online mode and only transmits or receives
data; it no longer responds to AT commands.
To return to command mode, to process AT commands for error
recovery purposes or to hang up at the end of a session, the DART 200
issues an escape sequence, or drops Data Terminal Ready (DTR) (if
possible) with an &Dn set up option specified. Refer to Escaping
through the control interface, p. 8-16 for details.