Using GNU screen for AT commands

[Tim Harvey]

Greetings,

I've often asked users I'm helping 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.

My apologies if this isn't the right place to ask this. I've googled
around for the past couple of hours and haven't come up with anything
concrete other than people saying to use a different app.

Thanks,

Tim