i cant interface NXP2148 with the GSM module. i have used the UART1 (through RS232 DB9 using RXD, TXD and ground) to interface with the GSM module at 9600. when i send the command AT<CR> through hyperterminal it accepts, sends back an OK when i SEND the same command through NXP2148 there is no response. my program is correct i have checked it at the hyperterminal. And i tried changing the cable also... but still no response. PLEASE HEPL!!!!
DO you have a proper RS232 transceiver in place?
Are you certain that the cable connections are correct? Remember that the modem is a DCE, and TX is an input on a DCE...
Does the modem require any/all of the modem control lines (RTS, CTS, etc)? If so, have you correctly implemented them.
"when i SEND the same command through NXP2148 there is no response."
That could be any number of things:
1. The MCU is not sending at all;
2. The MCU is sending, but it is not (quite) right;
3. The signal is not reaching the DCE;
4. The signal is reaching the DCE, but it's not listening;
5. The DCE is receiving the signal, but it is ignoring it;
6. The DCE is responding, but the response is not reaching the MCU;
7. The response is reaching the MCU, but your software is not (correctly) recognising it
etc, etc,...
Andy lists a long list of potential problems.
My question is: Have you used an oscilloscope and looked at the signals on the GSM side? What is the difference when your microprocessor tries to send to the GSM moden, compared to the case when you send from Hyperterminal?
If you do see a difference, you just have to backtrack to the source of that difference.
i got the problem... DTR signal should have been LOW only in my board it is about +9V. THANKs A LOT for your help...