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Old 08 July 2017, 21:51   #1
ross
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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
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Old 08 July 2017, 22:32   #2
Toni Wilen
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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
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Old 08 July 2017, 22:47   #3
ross
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Interesting, thanks Tony.

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

Bye!
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Old 09 July 2017, 07:44   #4
Toni Wilen
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Yes. (Find A500 schematics and check how CIA /CS lines are generated).
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