CIA doubts

ross · 08 July 2017, 21:51

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

Toni Wilen · 08 July 2017, 22:32

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, 22:47

Interesting, thanks Tony.

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

Bye!
ross

Toni Wilen · 09 July 2017, 07:44

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

08 July 2017, 21:51	#1
ross Defendit numerus Join Date: Mar 2017 Location: Crossing the Rubicon Age: 53 Posts: 4,473	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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08 July 2017, 22:32	#2
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,514	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

08 July 2017, 22:47	#3
ross Defendit numerus Join Date: Mar 2017 Location: Crossing the Rubicon Age: 53 Posts: 4,473	Interesting, thanks Tony. So an address with A12 and A13 active select both. Not that I want to do it Bye! ross

09 July 2017, 07:44	#4
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,514	Yes. (Find A500 schematics and check how CIA /CS lines are generated).

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