TDC interface panel

Hi ppl.
Just had an thought of building a little TDC panel for SH3. I never been good
at memory management and that stuff so im wondering if it possible to
change states and read them, i.e write a value to range in the TDC and
read the state of a tubes port or the depth of the sub?
Having a little app that talks to a com-port maybe.
It's just a brainchild and i have no idea if it's even something usable...