description of memory access via the address bus
All memory access is done here. Memory read/write enabled is checked and also
DATA-pins are controled.
Bank sizes should be either multiples of 16 kB or 4 kB and start at a 16 kB
respectively 4 kB memory boundary (adress divisible by 2^14 resp. 2^12).
z80-mon(1), z80-banks(5), z80-ports(5), z80-memory(3)