A relatively quick post today. I started back at work after the Christmas break, and I wanted to take my little Pi in to show my colleagues some of the things I have been playing with during the holidays. Last night, while I was getting my stuff ready I though I'd have one more try at getting the Prolific PL203 USB to mini-UART cable working. This time I tried it on a different computer - a laptop which I had never connected it to before. I started by downloading and installing the recommended driver before I plugged the cable in. I stuck my Linux SD Card into the Pi; connected the HDMI to the monitor so I could see what was going on; connected the Pi end of the cable to the right pins; and finally plugged in the USB end of the cable to the PC.
I could see the Pi booting normally on the HDMI screen, and best of all, I could also see it booting over the serial connection when I started a serial terminal session in MobaXterm. Once booting had completed I was presented with a login prompt on the serial port, so I logged in. Just for fun I also plugged in the ethernet cable and opened a ssh session. Best of all, this was all without plugging in the micro USB power lead. The Pi was happily running, communicating over serial and ethernet, and showing its status on the HDMI display, all with only the power coming over the mini-UART power lines.
Once I was happy that everything was working, I even tried it on the PC which had failed to work a few days ago, but into a different USB port. This one worked fine, now, too!
The next step is to get the UART cable working from bare metal so I can start to have some sensible input and output at last.