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
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