I want to connect my Asus WL500 Premium with the serial console. On the ASUS mainboard are UART connectors, RX, TX and GND. But the voltage level of those signals is 0..3,3v where RS232 use -12v..12v. If you would connect those ports together you would blew your ASUS mainboard. Fortunately most cell phone cables use TTL signal’s, the “cable” convert it to rs232 level (or Serial2USB level, as those cable uses an USB connector).
So I bought a cheap cell phone cable at Ebay, it was a data cable for a Nokia phone, CA-42 (or DKU-5). The pinout I found here.
Pin 6: FBus Rx/USB D+
Pin 7: FBus Tx/USB D-
Pin 8: GND –
be sure to use data GND and not charger GND!
You can verify your signal level with a multimeter: there should be a voltage level of 3.3v between GND and TX and 0v between GND and RX (you receive nothing) when the cell phone part is not connected. To test that you picked the right RX cable you may connect your RX and TX cable together and connect with an terminal program, each typed character should come back to the terminal.
On your ASUS mainboard, the TX level is also 3.3v and RX is about 2.7. Now connect the cell phone cable to the mainboard:
Cell phone cable mainboard
And you’re done. Connect with a terminal program with 115200 8N1 (Flow control off or XON/XOFF). I tried to connect with lower baud rate without success! And you may ignore the data garbage you’ll see when you connect you cell phone cable.