> > There is another way of doing it that removes the need for any pullups.
> >
> > Set the pins as outputs. Set the outputs to all ones. Now read them
> > and see which ones are high and which are low, and save the states.
> >
> > Now set all the pins as 0. Again read all the pins and compare the
> > states to the previous read. If the state has changed the output is
> > not connected to anything. If the state doesn't change the output is
> > shorted to somewhere by the dip switch.
> >
> >
> It is really abusive to short digital outputs high or low like this. Many=
 parts will
> withstand it, but it almost certainly exceeds the absmax ratings on the p=
ort
> outputs.

Abusive for a handful of microseconds (unless using an extremely slow clock=
)

In reality the abuse the output transistors will see is the short circuit c=
urrent specified in the data sheet for a very short time (unless the code i=
s badly written). I wonder how that 'abuse' differs from the current glitch=
 the same transistor would see driving a reasonable frequency signal (i.e. =
non-steady state). That is likely to be charging and discharging a capacito=
r at a rate that will cause a reasonable amount of 'abuse' to the transisto=
r.





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