Serial debug using "Silicon Labs CP210x UART Bridge" -- needs 3.3V connection

General Discussion
1

I’m using “Silicon Labs CP210x UART Bridge” to connect to Serial Debug header. The cable has 4 pins (GND, Rx, Tx, VDD). Since BBB uses only 3-pins (GND, Rx, Tx), I left VDD unconnected.

I could receive data from BBB, but I just couldn’t send any data. I tried Windows (PuTTY) and Linux (minicom), with the same result. As last resort, when I connected 3.3V of BBB to the VDD of serial cable, data flowed both ways.

Silicon Labs cable was cheaper than FTDI. Now, I know why.

2

4 pins are actually safer, they use vdd from j1 header to set and feed the voltage level on the ttl buffers for rx/tx.. with 3 pins you get a close voltage..