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-   -   CIA doubts (http://eab.abime.net/showthread.php?t=87842)

ross 08 July 2017 22:51

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 $

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?


Toni Wilen 08 July 2017 23:32

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

ross 08 July 2017 23:47

Interesting, thanks Tony.

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


Toni Wilen 09 July 2017 08:44

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

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