CIA doubts
 

Hi, lately I'm doing tests with CIAs.
And an academic question arised (in fact I have not read any manuals about it ;)).

The data lines usage (D0:7 for CIAA, D8:15 for CIAB) explain the odd and even address usage.
And can image that if in address space 64KB is 'available' address lines to select is $

bf

xxxx.

The question: both CIAs 'lives' in the same space? If yes, a word write cross both?
Or simply there is an assigned bit in address lines that select a single CIA?
But then for what reason they decided to split the data bus line usage?

Thanks,
ross

Yes. A1000 and Gary based Amigas can access both CIAs simultaneously (if both select bits are active). I don't know if it was designed to do that or if it is was only a side-effect.

Gayle and Fat Gary only allows single CIA select, only bfexxx or bfdxxx space activates CIA select line.

More detailed here: http://eab.abime.net/showpost.php?p=...&postcount=210

Interesting, thanks Tony.

So an address with A12 and A13 active select both.
Not that I want to do it ;)

Bye!
ross

Yes. (Find A500 schematics and check how CIA /CS lines are generated).