Discussion in "GSM and CDMA Discussion" started by    ravi23ganiga    Apr 3, 2014.
Thu Apr 03 2014, 04:50 pm
#1
I have the following query for the timing
of the inter at command

If i send any at command
say AT\r\n

and i get the response

<CR><LF>OK<CR><LF>

after getting this response
if immediately i send the next
command , many a times
i get ERROR from Modem,
but if i delay sending next command
the command works properly

So i wanted to know what is the minimum
time i need to wait after getting the proper
response from GSM Modem and sending
next command

I am using SIM900A GSM Modem
Fri Apr 04 2014, 12:20 pm
#2
GSM modems are very slow. For non network related command minimum delay for SIM300 is 250ms and SIM900 is 500ms. For Simcard related commands and network related commands it is recommended to keep 1sec delay atleast. Some network commands like CREG, CGREG and CSQ does respond within 500ms but still I advice to keep delay of 1s.
 ravi23ganiga like this.
Fri Apr 04 2014, 04:14 pm
#3
So If the code sends any AT command and if the modem gives
proper response for that AT command
then the code should wait for 1 second and then send the next
command

Is there any specific reason for this kind of modem behaviour
or can u suggest any reference document of the modem for
studying this kind of behaviour
Fri Apr 04 2014, 05:09 pm
#4
As I mentioned some commands are network specific and simcard specific. so they need time to process those command to actually provide you with a response. Consider modems as another embedded system that you're interacting with. so and modem has external inputs from peripherals and wireless network. so it needs time.

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