SYNC (which is active-low, BTW) is asserted ONLY for the opcode byte; it is deasserted for the operand bytes that may follow. Therefore, it is possible to use this, but the logic involved will need to be aware of which opcode is being fetched, so that it can "remember" the SYNC state for the ...

When I was at university, some of my clever fellows realised that it was possible to add write-only I/O devices to a system without losing any of the memory map. Simply enable the ROM for read accesses only and then re-use the same addresses for your write registers. Since the ROM was a 16k device ...

No news since june... Daryl, can You publish news every month, pleeeease.