So unlike the original Beagle Bone, which had a built in USB serial adapter, the Beagle Bone Black only has a serial header and you have to buy a USB to serial adapter to get a real serial console.
There’s one other option for a pseudo serial console over the USB On the Go port but the problem with this is that it doesn’t work with u-boot so only works once the kernel has booted as we can setup the port. The enabling and use of the USB OtG in Fedora is still on my ToDo list to investigate for ARM but we can possibly enable it as both serial and usb network at some point in the future.
So for now we need to use the 6 pin header to connect a USB to serial adapter. The most important thing to note here is that it requires 3.3 volts for the data signals so don’t use some of the older 5 volt units. The best USB to Serial to use is the FTDI FT232RL but at $20 it’s almost half the price of the device. The advantage is that it just works and the 6 pin connect just plugs straight onto the board (black goes to PIN 1). I’ve also tried the Adafruit 4 Pin Cable (PL2303), which at $9.95, is less than half the price and as the 4 pins are on 4 separate 1 pin headers it can be used on a number of different devices as it doesn’t matter how the serial headers are pinned out. To connect to The BBBlack the black wire goes to PIN 1 (Ground), the green wire to PIN 4 (Receive) and the white wire goes to PIN 5 (Transmit). The red wire is power and isn’t needed. CircuitCo has a number of other Serial Cable Options listed and the appropriate configurations for them too.
Now for a serial console app on Fedora I usually use screen. So simply once you have your serial console connected to the BeagleBoneBlack just plug the usb port into you computer and run
sudo screen /dev/ttyUSB0 115200 and then power up the Beagle Bone and you should soon see the output from u-boot and you’re on your way.