Re: [Lcd4linux-devel] =?iso-8859-1?q?display_on_WRAP-Board_-_how_fast?= =?iso-8859-1?q?_is_i2c=3F=09ho_w_good_is_the_lpc_connector=3F?=

[Ernst B. <e.b...@xe...>]

On Tuesday 25 July 2006 17:11, Stefan Krister wrote:
> Hi Luis,
>
> Luis.F.Correia schrieb am 25.07.2006 15:27:
> > For the sake of completeness, here's an update to the schematics:
> >
> > The PCF is powered by +5V, but the I2C inputs are biased to
> > +3.3v, which is the correct voltage level of the WRAP board.
>
> My datasheet says that voltage between 2.5V and 6.0V are valid. Must I
> provide 5V also? And where to take ...
>

The I2C chips usually connect to the bus using open-collector drivers, so its 
basically only important your PCF and the uC share the same ground.

(The chips can only drive the bus lines low, its pulled up only by the 
pullup-resistors)

Of course, you should connect your i2c-pullup resistors to the lowest Vcc in 
the system, in your case to 3.3V.

That way your i2c bus would operate on 3.3V, your PCF would work on 5V, but 
will still recognize the logic levels on the bus... As always, check the 
Datasheet to be sure.


HTH
/Ernst