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 Post subject: Why ...
PostPosted: Fri Jan 10, 2020 10:54 pm 
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... did WDC decide to replicate the 6522 rather than the 6526? Or even take the next step and produce both and drop the 65C21?

Seems to me the 6526 would be a more generally useful device.

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 Post subject: Re: Why ...
PostPosted: Fri Jan 10, 2020 11:17 pm 
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Well, I actually think the 8520 (as an W85C20) might even be more useful... with a 14MHz clock rating. I guess there's the possibility that WDC don't have the IP rights to some of the later chips that were used in the latter machines, which include the Amiga as well. I'm guessing someone might know... then again, I could just send email to Bill and see what he says.

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 Post subject: Re: Why ...
PostPosted: Fri Jan 10, 2020 11:40 pm 
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floobydust wrote:
... then again, I could just send email to Bill and see what he says.
Yes! If that is a possibility, then please. Knowledge is power ... or something like that. (Perhaps you could generalize the question, like why only the 6521, 6522 and 6551.)

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 Post subject: Re: Why ...
PostPosted: Sat Jan 11, 2020 1:48 am 
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BillO wrote:
... did WDC decide to replicate the 6522 rather than the 6526? Or even take the next step and produce both and drop the 65C21?

Seems to me the 6526 would be a more generally useful device.

I suspect WDC didn't do the 6526 because that was a Commodore Semiconductor Group (CSG) scratch design from the era of Jack Tramiel. Bill Mensch would have needed a licensing agreement from Commodore to legally produce a clone. There has been some off-and-on conjecture that Mensch didn't leave CSG (formerly MOS Technology) on the best of terms, which would have made unauthorized cloning of the 6526 a hazardous undertaking, lawsuit-wise.

As the 6526 was only a slightly-enhanced version 6522, I doubt there was a good business case for it. Also, it too had hardware bugs, two of them actually, one of which was more serious than the serial shift register bug in the 6522.

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(Perhaps you could generalize the question, like why only the 6521, 6522 and 6551.)

Back when WDC went into business, those three devices were the most widely used with 6502 systems. There was a market for them at the time. Nowadays, I suspect the overwhelming majority of uses for them is in hobby systems.

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 Post subject: Re: Why ...
PostPosted: Tue Jan 14, 2020 3:28 pm 
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BigDumbDinosaur wrote:
As the 6526 was only a slightly-enhanced version 6522, I doubt there was a good business case for it. Also, it too had hardware bugs, two of them actually, one of which was more serious than the serial shift register bug in the 6522.


Two bugs? Do you have some more details? Are you referrring to TimerB and TOD bug or something else?


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 Post subject: Re: Why ...
PostPosted: Tue Jan 14, 2020 7:53 pm 
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fhw72 wrote:
Two bugs? Do you have some more details? Are you referrring to TimerB and TOD bug or something else?

The timer and TOD bugs. The timer B bug was found to be in about 60 percent of the 6526s that were sampled. The TOD alarm bug was present in all of them, but has an easy work-around.

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