I have the Vlcd connected to +5V according to the datasheet.
The problem is, that the ic doesn't output any difference in signal
(i.e. pins and common planes are +5V, thus no segments turn on)

----- Original Message -----
From: M. Adam Davis <adavis@UBASICS.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, February 24, 2000 10:05 PM
Subject: Re: PCF8566 on PIC


> If you are saying that you don't have VLCD hooked up to anything, then
that
> could be the reason you are having problems.
>
> LCDs, due to their capacitive nature, require an AC signal.  Part of this
signal
> is often generated as a negative voltage, and often the VLCD is that
voltage.
> I've seen it range from ground to -15 DC.
>
> According to the data sheet, it needs to range between Vdd-6 and Vdd-2.5
VDC.
> If you are using a 5 volt power supply for the chip, then you can
/probably/ tie
> VLCD to ground, but you might want to create a -5v power supply, and
connect
> VLCD to a pot and resister combination which will allow it to range
from -1 V to
> 2.5 V.  This is your contrast control.  The chip will not do anything if
VLCD is
> left unconnected.
>
> You did not tell us what LCD you were planning on using, but they can
differ
> slightly in their driving specifications.  Read the LCD data sheet for
more
> info.
>
> -Adam
>
> > John Bes wrote:
> >
> > Hi,
> >
> > I have been trying to get a philips pcf 8566 (LCD driver) to work with a
pic.
> > I have two of them and they both don't seem to react, to any command.
> > Has anyone any experience with this ic?
> > The i2c-bus works fine (tested it with a scope).
> > I really need some help now, probably a coding error, I suspect, but I
can't
> > find it.
> > After the i2c bus transfer the common connection to the lcd outputs a
5Vdc and
> > it is slowly destroying my lcd's. :(
> > Maybe I should do something with the Vlcd? The datasheet isn't very
> > helpfull.....
> >
> > anybody out there who would like to help?
> > Thanx,
> > John
> >