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'[PIC] RA4 pin'
2005\10\16@105425 by Sam

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Does RA4 pin ( it is open-drain one ) should be grounded? I've read one
document saying that if it's left floating it can cause instabilities of
other ports.

Do you know anything about it?



Thank you,

Sam

2005\10\16@114322 by Maarten Hofman

face picon face
> Does RA4 pin ( it is open-drain one ) should be grounded? I've read one
> document saying that if it's left floating it can cause instabilities of
> other ports.
>
> Do you know anything about it?

It is best to make sure all ports that are not used are in a known
state. This can be done by either setting them to an output and
outputting 0 (1 is more likely to cause leaks, I think) or setting
them to input and attaching them to either ground or 5V, in both cases
using a resistor to reduce current flow in case you accidentally set
the port to output. Ports that are not in a known state could start
moving quickly back and forth between states, which would increase
energy usage. I doubt it would cause instability on other ports,
though you might notice it because of the read-modify-write cycle of
most port accesses.

Greetings,
Maarten Hofman.

2005\10\16@130512 by Gerhard Fiedler

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Maarten Hofman wrote:

>> Does RA4 pin ( it is open-drain one ) should be grounded? I've read one
>> document saying that if it's left floating it can cause instabilities
>> of other ports.
>
> It is best to make sure all ports that are not used are in a known
> state. This can be done by either setting them to an output and
> outputting 0 (1 is more likely to cause leaks, I think) or setting them
> to input and attaching them to either ground or 5V, in both cases using
> a resistor to reduce current flow in case you accidentally set the port
> to output.

If you configure port RA4 as output and set it to 1, it is a floating input
(without an external pull-up or pull-down resistor). If you set it to 0, it
is not floating (as the output driver is pulling the pin down to ground).
As Maarten and others said, floating inputs are not a good thing, so do
avoid them.

In a circuit where I don't use RA4, I usually find a place for a pull-up
resistor connected to it. This allows me to use this port as test output
(or input) during development.

Gerhard

2005\10\16@174449 by Jinx

face picon face
> Do you know anything about it?

http://www.piclist.com/techref/logic/xtrapins.htm

2005\10\16@204429 by Sam

picon face
Very useful.

Thank you,
Sam

Quoting Jinx <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz>:

>> Do you know anything about it?
>
> http://www.piclist.com/techref/logic/xtrapins.htm
>
> -

2005\10\16@205121 by Jinx

face picon face

> Very useful

http://www.piclist.com/techref/logic/xtrapins.htm

Oh, there's all kinds of useful stuff at piclist.com

Isn't that right James ? ;-))

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