The Messy80 has 32kb of EEPROM and 32kb of RAM, 8 interupts and 8 separate outputs to select external IO interfaces with up to 32 addresses each.
The board has header that expose the necessary input/outputs to expand the functionality of the Messy80.
On board there is a 16C550 UART and a UART to USB chip which is used as the standard interface.
The monitor program is written for zasm.
This is what the serial monitor looks like right now:
|0x8000||0x83FF||RAM, Reserved for monitor|
|0x8400||0xFFFF||RAM, For whatever, as long as it doesn't collide with the stack*|
* The stack is set up at 0xFFFF and grows downwards.
Start building circuits on the breadboard to interface with the Messy80
Connect a CF-card to the bus and write a simple flat filesystem.