Re: If you were to put a graphics chip on an apple II card...

[Michael J. Mahon <mjmahon@aol.com>]

<aiiadict@gmail.com> wrote:
> On Thursday, August 30, 2012 9:59:26 AM UTC-7, (unknown) wrote:
>> On Wednesday, August 29, 2012 6:58:37 PM UTC-7, Sean Fahey wrote:
>> 
>>> On Wednesday, August 29, 2012 7:03:04 PM UTC-5, (unknown) wrote:
>> 
>>> 
>> 
>>> 
>> 
>>> 
>> 
>>>> Looks like a good one to start with.  The Byte card looks simple enough..
>> 
>>> 
>> 
>>> 
>> 
>>> 
>> 
>>> Would it be possible to combine the Byte Card with an audio card
>>> (similar to the Arcade Board) except something more popular that had
>>> software written for it - like the Mockingboard?
>> 
>> 
>> 
>> Possible?  Anything.
>> 
>> 
>> 
>> The 9918 doesn't need any address decoding, it has device select and RW
>> which can be derived from the Apple II bus using simple 74xx logic.  There is no ROM.
>> 
>> 
>> 
>> Mockingboard...  I think it uses 6522 interface chip?  That wouldn't
>> need any address decoding either.
> 
> 
> Yes, http://en.wikipedia.org/wiki/File:Mockingboard_V1.jpg
> 
> Would be interesting to know how Arcade Board/ SuperSprite would address
> the chips seperately on a single card.  I haven't looked at the 6522 datasheet in a while.

Address decoding is actually trivial for peripheral cards, since $Csxx
space is already decoded and there are only 8 address bits to worry about.
Incomplete decoding is quite common, as with the 2x6522 Mockingboard. 

You'd want to keep the Mockingboard interface, since it actually has a
software base, and you could put the 9918/F18A in /devsel space, not having
to be compatible with anything. 

The one real PITA with the 9918 is that any access to its RAM must be done
indirectly by setting 9918 registers, which *really* slows things down. 
BTW, that was the *only* access to RAM in the TI 99 series!

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon