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gsm interfacing with microcontroller

srinivas katepalli

Hello sir/madam, My name is srinivas.for my microcontroller interfaing to GSM modem application, first i tested GSM modem with PC that time , i am getting a new problem while interfaing PC with GSM modem.when i am interfacing PC to GSM modem with total 9 pin DB9 connector RS232 cable, it working fine. But when i am interfaing GSM modem to PC with(Rx,Tx and GND) 3 pins , its not working. how i overcome this problem . please help me, bcoz for application i will provide those three pins only.i.e,when i will GSM interface to microcontroller , i will provide those three pins only.
please help me and if you give through suggestions this mail also oltc@inteluxindia.com.
Thank you very much.

  • 0

    "But when i am interfaing GSM modem to PC with(Rx,Tx and GND) 3 pins , its not working."

    Actually, it almost certainly is working!

    All modems (not just GSM) will use the full set of RS232 control lines - if you don't assert the required signals, the modem will correctly interpret this as a "command" to not communicate!

    Your modem may have an AT Command (or commands) to allow it to work with just the 3 wires - check the Manual - but many require certain lines to be active.

    If not, you will need to loop-back CTS to RTS at the modem:

               Modem       3-Wire cable to PC
TXD in  <-------(  3  =-----------------< TXD out
RXD out >-------(  2  =-----------------> RXD in

CTS out >-------(  8  =--+
                         |
RTS in  <-------(  7  =--+

GND ------------(  5  =------------------ GND


    You might also want/need to loop-back DTR to DSR:

    DSR out >-------(  6  =--+
                         |
DTR in  <-------(  4  =--+


    Again, check the modem's Manual

  • 0 in reply to Andy Neil

    Remember that you will also need a suitable RS232 Transceiver (MAX232 or suchlike) between your microcontroller and the modem...

  • 0

    "if you give through suggestions this mail also oltc@inteluxindia.com."

    If you want email notifications, then just check the 'Send me e-mail when anyone posts to this thread' option!