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Author Topic: GSM shield with SIM900 - problem with corrupted AT characters?  (Read 1390 times)
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Hi friends,
I tested arduino gsm shield with my SIM900 testing module. It is same as Q-M10. But I have some problems with communications. When I power on module and begin communication, module go to shutdown after few commands and program is STOPPED. Totally stopped.

When start routine reach AT+IFC command, program call module restart...
After module is powered off, program run is stopped. I laborated with this few hours and I find solution - when I disconnect SIM900 TX pin from arduino sw RX pin, program suddenly starts to run. I think source of this problem is in SW serial interupt. When is RX pin is HIGH, or is moved from H-L-H-L, everything is OK. But when is at LOW (module is off), program is waiting for some change on RX pin and is stopped.

Do you know some solution for this problem?

Code:
OK
AT+CGREG?

+CGREG: 0,4

OK
AT+CGREG?

+CGREG: 0,4

OK
AT+CGREG?

+CGREG: 0,4

OK
AT+CGREG?

+CGREG: 0,4

OK
AT+CGREG?

+CGREG: 0,4

OK
AT+CGREG?

+CGREG: 0,0

OK
AT+CGREG?

+CGREG: 0,0

OK
AT+CGREG?

+CGREG: 0,1

OK
C=1,1
AT

OK
AT+CGREG?

+CGREG: 0,1

OK
IFC=1,1

NORMAL POWER DOWN
[00]˙˙˙˙AT

This output i get directly from GSM module TX PIN with echo ON with UART/USB module. Very often I get corrupted "IFC" AT command. I receive i?-=1,ú or some wrong characters and module is restarted after this...

When I enable debug, everything is OK. I think this problem have a source in too fast communication to module. Is possible to enter some delay to end of each AT character? I want to try slower communication.

Many thanks for some tips. GSM shields looks very fine, but I need port this to SIMCOM modules for my project.

Petr
« Last Edit: May 23, 2013, 08:55:07 pm by darksir » Logged

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