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GSM phone and PIC16f628 - UART Tx-Rx lines of the pic

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Newbie level 3
Jan 27, 2003
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Hi guys,

I know my contribution to this forum so far is still on level zero, but I'm running against time to finish a university project on time. After that, I promise to be a contributor :)

Here's the problem: I'm sending AT commands from the PIC to the phone, using the built-in UART Tx-Rx lines of the pic, I see no response from the PHONE at all. I've checked the phone's interface (PHONE TTL -> RS232) it works, and also the PIC interface (TTL->RS232) works as well, both tested connecting them directly to COM1 with HYPERTERMINAL. The reason for why I have to change twice the voltage levels is because the finished project is meant to be able to connect to any phone using a standard serial cable.
The thing that makes me worry is..that maybe I'm not actually sending a "SEND" command after the actual AT command...
What I mean is, when sending from the HYPERTERMINAL the command
AT , then you press the ENTER key on the keyboard, and supposedly it sends <CR> and <LF>
I do the same thng from the pic, sending A, T, 0x0D, 0x0A
but I get no response from the phone...Any ideas guys?
This problem has waisted me 5 days so far, it drives me crazy...
Thanks for any help in advance

Best regards,


My recomendation never use hyperterminal for anything. My recomendation is WinTelix 1.1 or Telix 3.11 (DOS). Telix for DOS is better because you can use num keypad to send binary codes in Windows programs this doesn't work.

For connection with uC UART you can direct connestion. Make sure that speed, number of stop bits and parity are matched with uC UART settings.

You can set local echo in Telix Terminal but best way is to enable echo from uC (in UART interrupt rotine send received character for echo).

Check RS232 levels and cable & connector connection.

For RS232 levels testing you can make null modem shorting Tx and Rx on TTL/CMOS side of RS232 chip. Type some on terminal and check response. If you have response as you typed connection is OK.

After that you can check uC programm.

which phone are you using?


Anyone know the serial port settings for nokia mobile phones or nokia 3310 in particular I would like to interface to it

Nokia phones needs SDK from NOKIA. Use Siemens - 35i. Very good for interfacing. You can issue AT commands.


Did you connect power to the datacable ?
Only few datacables power the ic from the mobilephone accu.

When you use the cable with the PC
it gets the power from PIN 4 and/or
PIN7 of the RS232 connector.

that was one problem by using a avr and a mobile phone.

@ AT-Commands
All AT-Commands had to be finished with a 0x0D 0x0A.

First send a ATZ to reset the mobilephone, sometimes its very useful

Re: GSM phone and PIC16f628

zouganelis can you give me the circuit that you used for this project plz ?

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