Sierra Wireless DART 200 CDPD Modem - Manual (Page 105)

DART 200 CDPD Modem User’s Guide 8 Application Programming
PN1197-00 Revision 1.0 8-11
Escape transmit control
A default feature of the modem causing any data remaining in the packet
buffer to be transmitted before the modem returns to command mode.
The escape can be performed by the three-character escape sequence, or
by transitioning DTR with &D1 or &D2 specified. If your transmission
consists of a single packet, this technique can be used to forward the
data.
Usage considerations (for TCP and UDP)
Manual transmit control is appropriate if the data packets being built by
the MAS contain character data and always end with one or the other of
two characters (S-Registers 51 and 52). However, if the application
generates variable ending characters, such as a checksum after a data
block, or if it uses a variety of single byte control characters, such as
ACK, NAK, ENQ, EOT, and so on, manual transmit control is not
possible.
Automatic transmit control is appropriate for binary data, and also for
character data where the last, or only character sent is variable. This
mode causes the data to be transmitted regardless of what that character
is. However, the default for the intercharacter time-out (ICT) is 2
seconds. In most applications, waiting 2 seconds before sending data
could cause performance problems. Set the ICT (S-Register 50) to a
small (or minimum) value to avoid this timing issue.
Automatic transmit mode must be used if the information being sent is
binary as opposed to character data. Since an 8-bit binary data field can
represent any value from 0 to 255, it is possible that some legitimate data
could appear as one of the data forwarding characters. If manual data
forwarding is used, the data block would be transmitted prematurely,
potentially causing errors and erroneous operation.
Auto answer setup
The DART 200 can be set up to accept incoming connection requests,
either automatically (recommended) or with the ATA command:
1. A server must be active: in TCP use AT*A1 to activate the server
function; in UDP use AT*A2.
? ?
NOTE:
Auto answer is disabled
while DTR is inactive if
&D1 or &D2 have been
specified.
? ?
NOTE:
This topic has already
been covered for telnet,
and does not apply to
SLIP mode since data
forwarding is a function
of the TCP/IP stack
software employed by the
user.