I've got a quick question regarding the speccy multiface - I'm trying to come up with a paper design for the SAM. I am assuming that a multiface works by causing an NMI and then swapping its own ROM/RAM in place of the speccy ROM when the interrupt service routine gets entered (and hence the multiface code is executed). My question is about the PC that gets written to the stack by the z80 - clearly this is going to get written to RAM, exactly where being determined by SP. This is fine assuming the program being interrupted is using the SP sensibly - i.e. to implement a stack -- but what if it is playing silly buggers with the SP and some important section of memory gets overwritten? Is this just very unusual and tough luck when it happens? I'm trying to decide whether or not to guard against this by preventing the PC from being written to the SAM's RAM and catching the values in some special latches instead...
Thanks, Andy
