Timeline for z80 crashes after executing some instructions

11 events

when toggle format	what		by	license	comment
Dec 11, 2017 at 20:04	comment	added	C32		oh man my comment earlier was stupid. just connect rom's cs to mreq
Dec 11, 2017 at 18:27	comment	added	Tommy		Open collector probably implies the logical AND if two devices output at once? I'm no expert, apply a pinch of salt to that guess.
Dec 11, 2017 at 17:36	comment	added	user3570736		Ah, yeah. The Z80 puts A on the top half of the address bus in the OUT (00),A instruction. As soon as A wraps round to 0 this was pulling A15 low. The Z80 and ROM would then both be trying to write to the data bus at the same time, and I don't know what that would do but it probably wouldn't be good!
Dec 11, 2017 at 15:30	vote	accept	C32
Dec 12, 2017 at 12:05
Dec 11, 2017 at 15:28	vote	accept	C32
Dec 11, 2017 at 15:30
Dec 11, 2017 at 15:18	vote	accept	C32
Dec 11, 2017 at 15:27
Dec 11, 2017 at 15:17	vote	accept	C32
Dec 11, 2017 at 15:18
Dec 11, 2017 at 15:14	comment	added	C32		IT WORKS!!!! \o/ i put an or gate on /rfsh and /rd and then going to the chip select of my rom instead of just putting cs to A15 and it worked!!!!! i believe now i should or that with a15 too , to add a ram.
Dec 11, 2017 at 15:10	comment	added	Tommy		Except that, as per a precious commenter, doesn't the Z80's refresh counter count in its low seven bits only? Bit 7 is always whatever you loaded R with.
Dec 11, 2017 at 9:42	history	edited	tofro	CC BY-SA 3.0	added 145 characters in body
Dec 11, 2017 at 9:20	history	answered	tofro	CC BY-SA 3.0