Re: 6522 VIA inputs

Date: Fri, 21 Apr 2017 21:40:17 +0200
Message-Id: <>
> On 21/04/2017 11:11, wrote:
>> I want to output data to VIA port pins acting as inputs and started to wonder whether I should drive the lines HI (seems to work in tests but if the lines are in fact pulled up then it's presumably unneeded/undesirable) or rather tri-state my outputs instead.
> On 2017-04-21, at 15:48, smf <> wrote:
> Do whatever is easiest.

The easiest is driving the lines, because I already do it and it seems to work but changing it from driving into tri-stating is not much of work.

> The pull ups are rather weak & while they work when you disconnect an input, running a long wire that is tri stated into the chip is probably not a good idea.

I don't expect the wires to be long enough to have tangible influence but right, I see what you mean.

> 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? ;-)

SD! -

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Received on 2017-04-21 20:01:19

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