Dear friends my application is that when i give 3 ring to the gsm connected with controller one relay should be ON and if i give 4 ring to it another relay should ON. can any one help me with this and thanks in advance!!!!!!
As explained in the items linked earlier, the same applies to the analogue PSTN.
See my post about the WikiBooks "Serial Programming/Modems and AT Commands" in this thread: http://www.keil.com/forum/18696/