I’m in the midst of a project and was wondering if the bus
Arbiter / IO chip disables PORT access to the various peripherals from the Z80 or if it leaves that access available in addition to the memory mapped access? If it leaves it enabled could you get in a weird situation where the 68K is reading or writing the controller direction register while the Z80 side could be modifying it via PORT?
IO access differences in MD mode vs SMS
Moderator: BigEvilCorporation
-
- Very interested
- Posts: 2440
- Joined: Tue Dec 05, 2006 1:37 pm
- Location: Estonia, Rapla City
- Contact:
Re: IO access differences in MD mode vs SMS
Since it would require bus crossing, abitration will take place and one will wait while other finishes, there will not be a bus conflict happening.
Mida sa loed ? Nagunii aru ei saa
http://www.tmeeco.eu
Files of all broken links and images of mine are found here : http://www.tmeeco.eu/FileDen
http://www.tmeeco.eu
Files of all broken links and images of mine are found here : http://www.tmeeco.eu/FileDen
Re: IO access differences in MD mode vs SMS
AFAIK PORT accesses are not doing anything in MD mode.
Re: IO access differences in MD mode vs SMS
Yeah, I/O port accesses don't do anything. The memory map is completely changed between MD and SMS modes (Z80 outright uses the 68000 bus in SMS mode, that should give a good idea of how heavily it changes - I assume this is so mappers can see accesses to their registers?).
Also if I recall correctly, if you try to access the 68000 $Axxxxx region from the Z80 (as opposed to using IN/OUT), expect the whole thing to lock up.
Also if I recall correctly, if you try to access the 68000 $Axxxxx region from the Z80 (as opposed to using IN/OUT), expect the whole thing to lock up.
Sik is pronounced as "seek", not as "sick".
Re: IO access differences in MD mode vs SMS
Thanks for the info. I don’t suppose there are any die shots of the IO chip and Arbiter? That may make things a little easier on me.