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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.

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:

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.

Thanks to this nice guide!