Started off with the 6809 Multicomp since the 6809 and 6800 are pretty similar.

I/O Selects

There are two 6850 ACIA (UARTs) in the design. A jumper on the board selects the Video Display Unit (VDU) which is a built-in terminal. The VDU has a 6850 hardware interface so it looks like a ACIA to the CPU. The other selects a 6850 in VHDL.