Re: [PATCH] I2C update for 2.6.8-rc1

Adam Kropelin
2004-07-16T17:45:00Z

On Fri, Jul 16, 2004 at 10:17:03AM -0700, Greg KH wrote:
> On Fri, Jul 16, 2004 at 07:07:16PM +0200, Pavel Machek wrote:
> > Hi!
> >
> > > +menu "Dallas's 1-wire bus"
> > > +
> > > +config W1
> > > + tristate "Dallas's 1-wire support"
> > > + ---help---
> > > + Dallas's 1-wire bus is usefull to connect slow 1-pin devices
> > > + such as iButtons and thermal sensors.
> >
> > Just out of curiosity... are such devices really connected using one wire only,
> > or is it GND+5V+one data wire, or GND+power&data wire?
>
> I'm pretty sure it's just 1 wire, at least for the devices I've seen.

It's GND+power&data. The device derives its power from transitions on
the data line driven by the master. Consequently there are some fairly
strict timing requirements on those pulses. Some devices can also be
powered by a dedicated VCC line which generally allows the device to
respond faster. A temperature sensor IC, for example, can usually
complete a conversion cycle much faster when it has dedicated power.

--Adam