hello everyone , i am facing a strange situation. i simply sent AT<CR> to gsm modem but in response receive only CR and character A instead of proper response i.e. <cr><lf>ok<cr><lf> already tied DTE and RTS pins to +5v for handshaking.
with hyperterminal everything was ok but this is not the case with uc.I also read previous threads but nothing worked.
Any idea which can help?????
thanks n regards rishi
I take it that this is a normal GSM phone, and not a GSM module for mounting on a PCB?
A GSM module is using TTL levels (probably 3,3V or 5V for all it's signalling). A GSM phone is using RS232 signal levels, since it (at least with the supplied serial cable) is intended to connect to an RS232 port of a computer.
Most newer RS232 devices supports quite low signal levels, to reduce the power needed from battery-driven equipment.
Anyway, if the serial cable has a full set of handshake signals, then you normally can loopback the handshake signals, i.e. you don't have to supply any signal voltage to them. The phone puts out a signal that it is ready - and at the same time, that signal gets sent back into the phone informing it that the other side - you - are also ready. Just like a null-modem cable, but you don't cross the signals from DCE and DTE - you loopback the signals directly in the connector.
Posted a bit early.
Connect RTS to CTS and DCE to DTE on the phone.