I'm trying to reverse engineer a 2Wire ADSL modem/router, mainly for practice. I opened it and found a serial port (with a header conveniently already in place) but I'm not getting any useful data out of it, only gibberish. The device does work (well enough to present its web UI), only this port is giving me trouble.
Why I'm pretty sure this is the right pinout:
- No other pins/pads anywhere on the board output anything that looks like data
- If I short Tx and Rx, or connect to my terminal and spam spacebar, it fails to boot up (LED stays red)
- The one NC pin looks the same on the oscilliscope as when it's not connected (slight noise instead of a steady 0V or 3V)
What I've tried:
- Several baud rates: 1200, 1800, 2400, 4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800, 500000, 921600, 960000
- Various combinations of parity and stop-bit settings
- Connecting it to a USB FTDI adapter
- Connecting it to the serial pins of a Raspberry Pi
- Adding pullup and pulldown resistors to Tx
- Inverting the Tx signal in hardware and in software
- Leaving the serial ground unconnected
No matter what, the data that comes in is gibberish, or nothing at all.
On my scope it definitely looks like data, jumping around between 0V and +3.3V for ~1/4 second at power on, then going to +3.3V and staying there.
But I just can't seem to find any combination of settings and connections that give me any coherent output. Am I missing something?
(For the record, I do own this modem.)