Using screen to talk to modems via AT commands

[Tim Harvey]

Greetings,

I've often asked users I'm helping with modem support on Linux to use
GNU screen to issue AT
commands to modems to get their details (ie ATI), however I've noticed
this doesn't work for me anymore on perhaps newer modems and I'm
guessing its related to a missing stty setting relative to CRLF.

So the following works from bootup on an MC8790 for example:
# echo -e "ATI\r\n" > /dev/ttyUSB3
# cat /dev/ttyUSB3
ATI
Manufacturer: Sierra Wireless, Inc.
Model: MC8790
Revision: K1_0_2_8AP C:/WS/FW/K1_0_2_8AP/MSM6290/SRC 2008/09/17 14:00:22
IMEI: 352974021856935
IMEI SV: 3
FSN: D661380183210
3GPP Release 6
+GCAP: +CGSM,+DS,+ES


OK
^C

However if I use 'screen /dev/ttyUSB3 57600,cs8' I find that AT
commands are never recognized - I get no response from the modem as if
it didn't catch the right line termination.

Any ideas as to what's going on here and how I could use screen and/or
stty to resolve it or what the proper stty settings are to avoid this.

Regards,

Tim

Tim Harvey - Principal Software Engineer
Gateworks Corporation - http://www.gateworks.com/
3026 S. Higuera St. San Luis Obispo CA 93401
805-781-2000