> The easiest way to avoid this problem is to latch the NMI > request from the button and then wait for the CPU to take opcode > (/M1=0) dealing with the stack. The best are #C9 (RET) and > %11xxx000 (conditional RET), assuming the code uses RETs at all.
That's a very neat idea.... > [...] SAM doesn't allow to > disable all memory access from expansion slot, untill you modify > the SAM inside or use external CPU. That had been my thinking - disable the SAM's z80 and hang a different z80 off the back... then I could trap and memory writes before they reach the ASIC. > In case when the SP points to ROM, you could latch address lines > (A0..A15) with /M1=0. Then analyse the opcode at latched > address. Does a write to the ROM region not write to the underlying RAM? Andy
