Sierra Wireless DART 200 CDPD Modem manual Auto answer setup

DART 200 CDPD Modem User’s Guide 8 Application Programming

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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.

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NOTE:

Auto answer is disabled while DTR is inactive if &D1 or &D2 have been specified.

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.

PN1197-00 Revision 1.0 8-11