> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Olin Lathrop
> Sent: 03 March 2011 12:30
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] 1 wire parasite mode
>=20
> Manu Abraham wrote:
> > So, if the resistor is the STRONG_PULLUP, then why
> > mention in the software flowchart, that STRONG_PULLUP is required in
> > parasite mode ?
>=20
> Probably because it is.  In parasite mode the device gets its power
from
> the
> data line.  That data line therefore has to be able to source current
> within
> some range.  At the low end, it must source enough current to keep the
> device powered.  At the high end, it must not source so much current
that
> it
> and other devices on the bus can't pull the line low.
>=20
> When it's not operating in parasitic power mode, then the data line
> doesn't
> need to source as much current since it's not powering the device.
> Therefore the pullup can be more weak.

On a one wire bus the so-called "strong pull-up" is only applied very
briefly prior to communicating with a peripheral.  It is not a resistive
pull-up as such, since nothing is expected to pull the bus low when it's
applied.=20

Regards

Mike

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