* RAMDIS is asserted when ROM or RAM are active meaning no write through to ram behind.
* Menu code is at offset &3810 and is copied into RAM at &A200.
* Uses port FBF0 (outputwrite only), FBFF (input).
FBF0 decoding is:
1111 1011 1111 00xx
bit 4 is A12 on RAM
bits 5-7 are not used.
* Uses port FBFF (input).
bit 7 is used - not sure for what.
Decoding of FBFF is:
1111 1011 1111 11xx