Re: 8520/21

From: Segher Boessenkool <>
Date: Fri, 6 Mar 2015 08:50:22 -0600
Message-ID: <>
On Wed, Mar 04, 2015 at 06:29:34PM -0600, Jim Brain wrote:
> I am not disputing that they are different, I just cannot understand why 
> CSG would have taped out a simpler version of the 6526/8521 when they 
> already had a die for the 6526.

6526 and 852x are very different.

> I can understand doing the work needed 
> to move the 6526 into HCMOS II, but why not go straight to the 8521, so 
> the resulting part could be used for the 64c/128/1571/1581/etc.
> It just does not make sense.  It's like saying:  I am going to modify my 
> iOS app for iOS8 and I am going to remove some key functionality, and 
> retest the entire app, since that functionality could affect any part of 
> the app.
> There has got to be more to this story.  I don't buy that the TOD BCD 
> stuff took up that much die real estate, and so I can't believe that the 
> removal would have improved yield considerably.

About half of the 8521 layout is wasted space anyway; space is not the
issue.  The 8520 has a TOD just fine as well -- but a binary counter,
not a BCD counter.  A BCD counter does not take up much extra space,

Presumably they just wanted a binary counter for the Amiga.  The idea
that they made the 8520 and then the 8521 was an afterthought might be
true, too :-)


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Received on 2015-03-06 16:00:07

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