Re: 6522 VIA inputs

From: Segher Boessenkool <>
Date: Sat, 22 Apr 2017 17:54:58 -0500
Message-ID: <>

On Fri, Apr 21, 2017 at 09:38:27PM +0200, wrote:
> > On 2017-04-21, at 19:12, Mike Naberezny <> wrote:
> >> Take a look at the MOS datasheet for the 6522 (If you can't find it, I can mail it to you), it has schematics for the port drivers for port A and port B, they differ, but both ports have a permanent pullup in form of a MOS transistor for each bit.
> Yeah - thanks. I had only the Rockwell's one at hand with a somewhat misleading caption but it shows more or less the same, except that it shows a resistor instead of transistor. A cursory glance, together with the caption made me initially believe it to be only the output part and a kind of a final output stage inverter. The MOS and Synertek documents seem to be more accurate, even if their captions also talk about output only. I even downloaded the half-gig heavy MOS blueprint scan of the 6522 and it agrees with the MOS datasheet.
> > The MOS 6522 datasheet can be downloaded from here:
> >
> > 
> > The port drivers are on page 3 of the PDF.  The Rockwell and Synertek 6522 datasheets are also on
> Got those, thanks.

The datasheet shows a depletion-mode FET (with source tied to gate) for
the pull-up / keeper.  The schematic agrees, and so does the chip.  The
schematic shows a depletion-mode FET for the high-side driver as well,
and that is what is on the chip; the datasheet shows an enhancement FET
instead though.


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Received on 2017-04-23 00:00:02

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