problem with response of at commands

[micro_elec_90]

Hello everybody.
I have a sim900 module doesn't response to at commands. It meens in hyperterminal when I type any at command and press Enter it doesn't show the "Ok" for example.
But in interfacing with AVR I can send SMS. This meens that module receives our at commands from micro and do them but doesn't send response of the at command through the UART to micro.
In others words maybe module receive at commands through UART and do its job but doesn't send back response to the micro or PC in interface with hyperterminal.
I think there are some settings for module to send back the response or not or how to send back the responses.

Can anyone help me?
Thanks.

 

[horace1]

is the sim900 connected to a micro which is then connected to a PC?

if so it is possible that the micro is not receiving the sim900 characters correctly or if it is receiving them OK not transmitting correctly to the PC - in particular what baud rates are you using for the two communication channels - the same or different?

if you connect the sim900 directly to a PC do you get the sim900 response correctly?

 

[micro_elec_90]

Hello horace1 and thanks.

No. Sim900 is connected to a micro.

I don't know exactly how the module send back the response. For example after this code i have OK on LCD connected to the micro :

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Code C - [expand]
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printf("AT\r\n");
while(buffer1!='O')
buffer1=getchar();
while(buffer2!='K')
buffer2=getchar();
lcd_clear();
lcd_putchar(buffer1);
lcd_putchar(buffer2);

---

And also when i send module an SMS micro receive characters RO from module instead of +CMGR:

Is there any settings for the sim900 about how to send back the response?

Also when i connect the sim900 module to PC i don't get sim900 response correctly? Do you know why?
Thank You;

 

[horace1]

are the baud rates of the two UARTs different? I generally have them the same or the PC faster than the connection to the sim900, e.g. sim900 at 9600baud and the pc at 56700. If the PC connection is slower than the connection to the sim900 you can loose data with the PC getting overruns.

don't understand why the sim900 does not work when connected to the PC - are you sure you have the Rx and Tx lines the correct way around?

 

[micro_elec_90]

Do you know what is the response of the module after receiving an sms and sending "AT+CMGR=1" from micro to module?

 

[horace1]

Do you know what is the response of the module after receiving an sms and sending "AT+CMGR=1" from micro to module?

it returns the SMS message at index position 1

for an example see
https://www.developershome.com/sms/cmgrCommand2.asp