The board has a 6 pin header (marked J1 on my BBG and my BBB) that is parallel to and very close to P9. You need to connect to 3 pins on this header. Hold the board with P9 close to you and the network jack on the left. The 6 pins are:
There are many USB to serial gadgets that can be used. I buy cheap CP2102 based things from China for $2 each. These usually will not directly plug onto the BBB though and some fiddling is required. The following are more expensive, but perhaps more convenient.
I use picocom on my linux system, with the following command:
picocom -b 115200 /dev/ttyUSB0The actual USB serial device may be different, depending on your system and what other USB gadgets you have plugged in. Some people like "screen" instead of picocom. If you use windows, you may find Putty useful.
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