Changes

Expansions bigger than 512K extend that above standard. The LSBs of the 64K bank number is kept in D5-D3 data bits (as above), the MSBs of the 64K bank number are in A10-A8 address bits. Typically in inverted form (so the first 512K block is accessed via Port 7Fxxh, the next via 7Exxh, etc.

aaa = upper bits of 64K bank selection (512K-step) (A8,A9,A10 bits)

bbb = lower bits of 64K bank selection (64K-step) (D3,D4,D5 bits)

xxxxxxxx = should be set so that it doesn't conflict with other ports (*)