gday... just downloaded datasheet and had a look. You state u tried a max232 in your design... why? The logic level on the mc35 is 3V =>> a max232 will step it up to twelve, possibly damaging the modem!!
"
The electrical characteristics do not comply with ITU-T V.28. The
significant levels are 0V (for low data bit or ON condition) and 2.65V (for high data bit or OFF
condition). For electrical characteristics please refer to Table 22.
MC35i is designed for use as a DCE. Based on the conventions for DCE-DTE connections it
communicates with the customer application (DTE) using the following signals:
Port /TXD @ application sends data to the modules /TXD0 signal line
Port /RXD @ application receives data from the modules /RXD0 signal line "
I hope 4 ur sake that you haven't damaged ur modem. The pic's pins should be wired directly to the modem (unless, of course, you are using the interface board, and not the socket itself.)
The PIC should be running on 3.3V (or about that)... if you're using 5V, you might want to use voltage dividers on the PIC's outputs to ensure that you don't stuff your modem (inputs will still work).
To wire it up : PIC's TX pin goes to the RXD0 Line and the RX pin goes to the TXD0 pin (try swapping these though... the manual is rather ambiguous). Then, you have to implement the handshaking (HW) - or you can "spoof" it.
Read here :
http://www.zytrax.com/tech/layer_1/cables/heavy.htm
I would recommend that you wire RTS to CTS to spoof that signal. (I assume know to use a common ground for the modem and the pic). Wire the DTR0 pin to DSR0 pin and the DCD0 pins (all three together). I know that's not clear, if you don't understand, post back.
Also, ensure the command you send is "AT...\r", not "AT...\n", as cr is used instead of lf.
Hope that helps.
Feel free to email or msn me : beatonj -AT- gmail.com
--jb