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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
Avoid any attempts to throw away some characters in the middle of an ongoing communication. You will never know if you are close to the reception of the next character, i.e if different runs of the program may result in a character sometimes being received, and sometimes not.
@ Andy and Westermark.. yes now i am going to use interrupts for receive operation definitely...and let you know the results as soon as my ongoing college exams finishes.... you people really give me a new way to think .... OH! one more thing.. currently i have tied RTS nad DTE to +5 volts(valid RS232 level) to fool my modem that handshaking is provided...do i need to increase this voltage like +9 or +12 volts usually used in RS232...i checked in serial port of my pc and it gives 11.23 volts at RTS nad DTE...
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.