On 04/22/2017 05:19 PM, groepaz@gmx.net wrote: > On Saturday 22 April 2017, 17:12:10 Gerrit Heitsch <gerrit@laosinh.s.bawue.de> > wrote: >> On 04/22/2017 04:35 PM, groepaz@gmx.net wrote: >>> On Friday 21 April 2017, 21:40:17 silverdr@wfmh.org.pl wrote: >>>>> It's perfectly acceptable to ignore the pull ups and drive 0v/5v. >>>> >>>> I am not sure if I am not trying to overengineer but what causes my >>>> doubts >>>> is that it's never 0V/5V, and especially never the same between different >>>> families of devices, etc. While pushing the (pulled-up) line LO is OK >>>> because that's what it is meant to be done, the potential of the sourcing >>>> output and the pulled-up line are almost certainly different so it will >>>> have to cause some (unnecessary / unnecessarily higher) current flow >>>> through the line, possibly adding to consumption, unwanted emissions, >>>> etc. >>>> ... or are all those possible side-effects fully negligible and I am just >>>> too paranoid here? ;-) >>> >>> driving a NMOS i/o line high is a big nono. just dont. its a common thing >>> to do to connect several outputs together, forming a wired OR - when one >>> of those outputs is driving high, the one trying to pull low will have a >>> hard time doing it. even if it still may work, the signal timing will go >>> poop >> Eh? So far I though NMOS is very good at sinking current to GND, but not >> at supplying current from Vcc. Looking at the datasheet for the 6526 >> supports this, the output driver can supply at most 1mA, but can sink >> something in the range of 3mA. >> >> So if you connect 2 NMOS outputs together, the one pulling the line LOW >> will win. Also, on most NMOS outputs, you cannot disable the 'pullups' >> (see output driver schematic for the 6522). >> >> What you must not do is using a CMOS output set to HIGH and connect it >> to an NMOS output set to LOW. > > thats what i ment with "driving high". a NMOS output does never "drive high", > it only ever pulls low. The output driver for the B ports on the 6522 disagree. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2017-04-22 16:02:18
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