Open Drain means there is nothing to pull the output up to +5V inside
the uC.  That allows a number of devices to share that output and any
one device can pull it low without damaging the others.  To see a logic
high output you need to tie the pin to +5V through a 2K .. 50K resistor.

John Dammeyer



Wireless CAN with the CANRF module.
http://www.autoartisans.com/documents/canrf_prod_announcement.pdf
Automation Artisans Inc.
Ph. 1 250 544 4950


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Pic Dude
> Sent: Tuesday, May 14, 2002 4:56 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: Port A output woes
>
>
> I did come across "open-drain" in the datasheet, but
> did not fully understand its implications.
>
> So you're suggesting that it will float (or close) for
> logic 1 output, and actually go to low for logic 0 output.
>
> I can live with that.  All I'm using it for is some
> extra debugging indicators right now.
>
> Thanks,
> -Neil.
>
>
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Tony Nixon
> Sent: Tuesday, May 14, 2002 6:27 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: Port A output woes
>
>
> Pic Dude wrote:
> >
> > I must be doing something wrong here, but the problem eludes me...
> >
> > Using 16F872, Port A is setup as all outputs, and all digital, but
> > when I write 0xFF to Port A, RA<4> does not come go high.  I've
> > tested the LED, the resistor, and even the breadboard connection
> > by jumpering a wire from the IC pin to the LED.
>
> You're not doing anything wrong as such.
>
> RA4 is an open collector output and can only pull low. It goes open
> circuit otherwise and if you need a logic 1, you need a
> pullup resistor.
>
> Check out the PORTA info in the data sheet to see more.
>
>
> --
> Best regards
>
> Tony
>
> mICros
> http://www.bubblesoftonline.com
> mailto:sales@bubblesoftonline.com
>
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>
>
>

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