portb pull-ups

[flawed]

Hi all, Could somebody please help me with this.....

i have 6 input lines all held at 3v going into portb of my pic, - and these 3v inputs have a different power source and ground from the pic circuit. The problem is i only want to address one input at a time, but they all all held at 3v - which i cant change.

I was wondering if i could somehow sink this current via the pic. I've read on the data sheet you can enable pull up resistors on portb using the option register, but from there im abit lost. what i really want to know is - is there anyway to pull an input signal to ground?

thanks in advance for any replies.

 

[Gayan Soyza]

From where the inputs coming? Through a Schmitt trigger or else?

Sometimes I configured 555 ic as a Schmitt trigger & feeding its output directly to the PIC input pin it works & no internal pullups enabled.

 

[flawed]

it's a pull down i need really. there is a high signal present on each bit of portb constantly, but i would like to be able to sink these high inputs to the pic connected ground through software, because using a series external transistors as pull-downs is going to be quite clunky. looking at it i don't think i'll be able to do it with a pic, but if you have any ideas of how it could be done, im all ears!

cheers.

 

[Pommie]

A pic pin when set to output can sink 20mA. You don't say what you want to achieve except that you want to ground the signals, so, do that, connect the signals to the ground pin. Now you have the signals grounded, what do you want to do next.

Can you see why your post is confusing.

Mike.

 

[Gayan Soyza]

Your high signal you told that is 3V.You can configure a PIC input pin as an active low or active high input.

I'm using internal weakpull ups when connecting small switches & configure them as active low inputs.

When I receive signal from any IC or any transistors I configure them as active high inputs & no internal pullups used.

 

[flawed]

its cool, i've figured out how to do it. cheers tho guys