The UART Plug contains a hardware serial port with 64-byte buffers for both send and receive. It can support baudrates up to 115200 baud, if the connecting bus can handle this bandwidth.
An I2C bus running at 3.3V is used as interconnect, with all the power and signal lines brought out to to both sides of the board to allow daisy-chaining with other I2C-conformant boards.
The two solder jumpers on the board select addresses to allow up to four UART Plugs to be used together on the same I2C bus.
The pre-assembled version has the SMD-sized SC16IS740 serial chip, resonator, and capacitor already soldered onto the board. Note that no 6-pin headers are included.
The PCB only variant contains just the board for the UART Plug. No parts, no headers.
As connectors you can use a Plug Headers set with 10 male and 10 female 6-pin headers, which makes it easy to connect multiple plugs and JeeNodes in a “standard” way. Or you can solder the board directly in place for more permanent use.
The documentation and full design details are freely available.