Changes

* While the syntax of the 8-bit ADD, ADC and SBC instructions all explicitly mention the A register, the SUB instruction does not mention it. On the Zilog eZ80, the SUB instruction explicitly mention the A register.

* The Z80 has a lot of 8-bit registers but it can only really do arithmetic on one of them, A.

* IN r,(C) and OUT (C),r instructions syntax is misleading as these instructions actually use the full 16-bit port address contained in BC. On the Zilog eZ80, these instructions are correctly named IN, r,(BC) and OUT (BC),r.

* The Amstrad engineers chose to use the high byte of the address (register B) for chip selection instead of the low byte (register C) in I/O operations. As a result, OTIR / OTDR / INIR / INDR instructions cannot be used on Amstrad CPC for transferring or reading a sequence of values on a port, as these instructions use the B register as a counter.