I still don't support 132 mode but switching clears the screen, homes the cursor,
and clears any scrolling regions, so it's necessary for passing the vttest suite.
This is fixed in ROM 3 (or via the TS patches if you boot GS/OS).
Workaround it by switching to DPAGE 0.
Also, allocate memory (since I originally thought that might be relevant).
this also adds a hexdump in the CDA for the outgoing buffer
in local mode, "incoming" data is read from the outgoing buffer.
Currently data is (potentially) sent on each run of the main loop.
I thought about using the TX empty interrupt but it still needs to be
kicked off at some point (unlike incoming data)
