I am connecting GSM 900A module with PIC microcontroller and show their response on LCD. I have two GSM SIM900A modules. First GSM module is properly working with LCD. When I use second GSM module, its working but doesnot show any response message on LCD. That means LCD is good but not work with second GSM. Also there is no problem in communication section, otherwise its not work with first GSM. I only replace first GSM with second one and other connections remain same. The echo and response messages are shown for first GSM and not for second GSM. The program used in both cases are also same. When I made a call to second GSM module, I can hear the ring but LCD does not show anything. What is the reason? Please help me.
Thank you guys it's working now. I used a 3.3V to 5V level converter in between GSM module txr pin and PIC rxr pin. Now it's shows response message on LCD.