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Interfacing GSM using AT89S52

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apache79

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Hi,

I am interfacing a GSM Module with the help of a AT89S52 Microcontroller. I am writing the program on C and compiling using Keil.

I have tested the module on the computer and it works fine.

But when I try to generate a call through the MC, it doesnt happen. I tried debugging and found that the MC is sending some symbols and not the predefined code.

Please could anyone tell me how do I generate a call through the MC using AT commands and how should I enter it in the C program.

Also please could you tell me about the RS232 connections. I connect pins 2 and 3 for the Tx and Rx and pin 5 to ground. Should I do anymore connections on the RS232?

Any help on the above would be highly appreciated,

Thanks
 

In the place of the GSM module connect a PC with a serial terminal program like Hyperterminal.
Chech the AT commands comming from your microcontroller on the screen
 
Thank You for the reply, The AT command is being generated on the hyperterminal screen.

But when we connect it to the Module then the call is not generarted. The Module is indicating that it is functioning on the network correctly.

We are connecting Pin 2 for Tx and Pin 3 for Rx and Pin 5 on Ground from the RS232.

Could you please tell us, what we are doing wrong. Should we connect anymore pins on the RS232? Or is there anything else to do for it to work?

Thank You for your Help.
 

If the pins connections work with Hyperterminal then they are correct
 

I am connecting it to the computer using a RS232 Cable, but I am connecting it to the mgsm module using 3 wires which connect to the Tx, Rx and Gnd.

Should I connect something else?
 
Disable the modem auto baud rate :
1. Connect Modem to PC and start your terminal
2. Change Flow Control by typing "AT+IFC=1,1"
3. Save config with "AT&W"
4. Change baud rate from auto into your desired baud rate. e.g. 19200 by sending "AT+IPR=19200"
5. Save config with "AT&W"
6. Short RTS and CTS at GPRS modem
 
yes your rs 232 connection is correct first of all u try to call that number is placed in gsm sim300 modem to check if it works properly or not, then bye sending the command ATDXXX; to sim300 call a specific number .......
 

Did your modem registered to network successfully?
Confirm it by calling to the modem from other mobile.

Did you send <cr><lf> after the AT command?
CR an LF are control characters, respectively coded 0x0D (13 decimal) and 0x0A (10 decimal).
 

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