Hi! On Fri, Apr 21, 2017 at 09:38:27PM +0200, firstname.lastname@example.org wrote: > > On 2017-04-21, at 19:12, Mike Naberezny <email@example.com> 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: > > http://6502.org/documents/datasheets/mos/ > > > > The port drivers are on page 3 of the PDF. The Rockwell and Synertek 6522 datasheets are also on 6502.org. > > 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. Segher Message was sent through the cbm-hackers mailing listReceived on 2017-04-23 00:00:02
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