See notes below...
/Jan-Erik.


James Nick Sears wrote :

> This is what I am not sure about though.  Let me give an
> example to explain
> where I am not clear.
>
> Say for simplicity we are concerned with RD0:
>
> So when the reference is off (initial condition) we have:
> TRISD = xxxxxxx1 (x = don't know/care)
> PORTD = xxxxxxxx
>
> But RD0 as an input will sample the low voltage from the
> unpowered IC input
> and put PORTD,0 to 0 so we have:
> TRISD = xxxxxxx1
> PORTD = xxxxxxx0
>
> Now it's time to power up the IC - there are two options:
> (1)
> Set PORT register before TRIS register:
>     Set PORT register:
>         TRISD = xxxxxxx1
>         PORTD = xxxxxxx1
>
> Right here is where my question arises.  Since there is a low
> voltage connected to the pin which is configured as an input,
> then won't the PIC just sample the pin low and overwrite the
> change I just made?

No, the PIC doesn't "sample" anything if you don't ask it to, by
executing some instruction that *reads* PORTD. Note that, as shold
be clear from the data sheet, the write-part and the read-part
of PORTD is actualy two different things. And there is no direct
connection between them either then by doing a read/write from
your code.

>
>         So if I set TRISD = xxxxxxx0
>         PORTD might already be overwritten to = xxxxxxx0

Overwritten by what ?
Only if your code does something that writes to PORTD !

Such as doing a BCF/BSF to *ANOTHER* PORTD-pin, which
is exactly what all this r-m-w thing is all about !

Regards
Jan-Erik.

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