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!!!!
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.