Pullups and pulldows

[mackrackit]

I agree with Rob.
You can have an external pull up or down and still do what you want.
Think of it like this.

If you had a switch connected to a pin (input) that is set to receive a high signal when the switch is closed you would have a pull down resistor to hold the pin low so not to give a false reading.

If you had a mosfet or relay connected to a pin (output) that is set to go high to activate the mosfet or relay you would have a pull down resistor to hold the pin low so not to have the mosfet or relay coming on when is is not supposed to.

The thing I will suggest in your case is a 100K pull down might be better. It should increase the sensitivity.

[mister_e]

Problem when switching internal-pull up could be some false interrupts events. Your software MUST compensate for it. But i see no advantage to do so.... too bad... i can't take beer 'till few months ... in some occasion, it's an eye opener

[mackrackit]

too bad... i can't take beer 'till few months ... in some occasion, it's an eye opener

HUH? No beer? Whats up?

[mister_e]

Long story PM or e-mail....

[mackrackit]

What will happen when the 5V output is sent. As there is a 10K weak pullup connecting the pin to the ground... I guess some current will sink to the ground but most of it will reach the target pic, right?

Yep, that is why I think a 100K might be better in you situation.
I think

[mister_e]

I'm kinda lost in here... sorry And there's some danger also.. unless you also use a current limiting resistor between your PIC and the mag.... hence why i asked for a schematic awhile back... and weak pull-up can't be tied to GND... unless it would be pull-down.

[xnihilo]

I will make a schematic/diagram with the stuff by draw it by hand will be a mess. I will try to understand how to use EAGLE pcb designer so I make some decent diagram.

In the meantime, as I said, the two pics have to communicate using each one porta pin.

The communications is:
Gun-PIC send +5V to Mag-PIC who then turns its pin as output and sends back a +5v to the Gun-PIC.

I'll make my schematics and system description and source available on my website by the end of the week.

Anyway THANKS a lot for your help guys.

[xnihilo]

I'm kinda lost in here... sorry And there's some danger also.. unless you also use a current limiting resistor between your PIC and the mag.... hence why i asked for a schematic awhile back... and weak pull-up can't be tied to GND... unless it would be pull-down.

Sure, pull-down because I use the pin in low state so to avoid the pin to be left floating I tie it to GND, I read it is a good practice.