reZet80 SCOUT - I/O, display and keypad

The reZet80 SCOUT is a single-board computer (SBC) that provides very basic input and output capabilities.
A 74LS139 demultiplexer addresses one input and one output port:

Two 74LS244 buffers are used for the ports.
The output port is connected to two 7-segment common-cathode displays.
The input port provides the connection to a 20-key keypad for hexadecimal input.
Four special keys (ENTER, BACK, ESC and SHIFT) are also connected.

So the reZet80 SCOUT enables you to input and output hexadecimal numbers (for now).
The ports could be used for other purposes, too.