JTAG programming header for USG v1.0

The JTAG programming header is an optional accessory for the USG v1.0. It allows you to connect a JTAG programmer to the USG's circuit board, so you can develop and debug the firmware.

More information here:

https://github.com/robertfisk/USG/wiki/JTAG-Connection#v10-hardware

You don't need this if you just want to update the USG's firmware. You can do that with a USB cable instead:

https://github.com/robertfisk/USG/wiki/DFU-Firmware-Upgrade