Topic: Pull up?
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Location: Manchester (England England)
Solder is electric glue
Re: Pull up?
Aug 13, 2011, 09:21 pm
noobs" don't understand that it's better or somehow more correct to use a pull-up.
Yes that is correct.
We are not switching power here the rules are different. Imagine a switch on the end of a wire. If you use this to pull up the two wires are the 5V and the signal. However if it is the pull down, the two wires are ground and the signal. It is much safer to have long runs of ground that long runs of the power rail. It also the interference it picks up is much less damaging. Also an accidental short of a ground is much less damaging that shorting the power.
Finally with a lot of logic technologies it takes mush less current to switch to ground and pull up than the other way round. For example with TTL logic the maximum pull down resistor is about 220R where as the maximum pull up resistor is about 10K.