Mcgee, Mark wrote :

> > No, the PIC output is drives activily both high and low, so
> > no need for any pullup/down res.

> That's good news.  Is this documented anywhere do you know?  
> It's not that I doubt you, it's just that I couldn't find anything
> like that in the data sheet.

It's there...
(Chap 5.0 "I/O PORTS")

> > > Q3) I am using RA2,RA3,RA4 as inputs from 2 control lines and 
> > > a toggle switch.
> > > Shall I just hook them up to the inputs?
> > 
> > Yes, you could, but it also depends on the environment
> > where this design is to be used.
> Like what?  My project is going to run at ambient temperature 
> in a garage, controlling a refrigerator or heater to control the 
> temperature of beer fermentation.

Could have been in a car, or at the Northpole, you never said... :-)

> 
> > 
> > > Do I need pull-up/pull-down resistors?
> > 
> > If switch connects to 0V, you need pullup resistor.
> > If switch connects to 5V, you need pulldown resistor.
> ok, yes, makes sense.  The switch is connected to +5v, so a 
> pulldown resistor - will 100k be about right?

Again, depends on the environment. If very electricaly "unclean",
a lower value would probaly be better, 10 or 47 kohm maybe.
And, it's usualy more common to connect the switch to GND and
use a pullup resistor.


> 
> > > Looks like PORTA pins can sink 25mA, so that's 5/0.25=20R, right?
> > 
> > Only *output* ports can source or sink *any* current.
> > Input ports just "monitors/sense" the level on the pin.

> Oh.  I thought source was for output, and sink was for input. 
> Can you explain the difference to me?

"Sourcing current" is when an *output* pin is high and current flows
*out* from the pin through a load to GND.

"Sinking current" is when an *output* pin is low and current flows
from (eg.) +5V through a load *into* the pin.

But in this case you was talking about an *input* pin, not ?
Input pins never either source or sink any current.

Best Reagrds,
Jan-Erik.
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