OK, this is a good idea. Cheaper solution would be power the PCF8574 at 5V and adapt levels only on the SCL and SDA lines (as suggested Frédéric too). Thank you everyone for the answers. Now I know that voltage adapters between 3.3V and 5V logic are the "clean way" to do the work, but maybe a lot of applications (like that reported on the amcesystems's site) run well without them!
Maurizio 2007/1/24, John Crispin <[EMAIL PROTECTED]>: > > add a bus driver between pcf8574 and lcd then > > Quoting maurizio bertero <[EMAIL PROTECTED] > <maurizio.bertero%40gmail.com>>: > > > Hi, > > you suggestion colud be true, but if I power the PCF8574 at 3.3V I move > the > > problem to the LCD which is 5V powered. Again, there is no assurance > that > > the 5V powered LCD can recognize the 3.3V levels generated by the IIC > > expander..... > > > > Maurizio > > > > > > > > 2007/1/23, Geert Vancompernolle < [EMAIL > > PROTECTED]<geert.vancompernolle%40hotpop.com> > >: > >> > >> --- In [email protected] > >> <foxboard%40yahoogroups.com><foxboard%40yahoogr > oups.com>, "maurizio > >> bertero" > >> <[EMAIL PROTECTED]> wrote: > >> > > >> > hi, > >> > I've got one question relative to the article "Using the I2C driver > to > >> > access a HD44780 LCD" (http://www.acmesystems.it/?id=162). > >> > The schematic seems don't care about different logic levels between > >> the fox > >> > board (3.3V) and Philips PCF8574 (5.0V). > >> > I know that Fox's inputs are 5V tollerant so no damage will happen, > >> but I > >> > have some doubt regarding the ability of the PCF8574 to regognize > output > >> > levels coming from the FOX (i.e. the I2C clock signal). The PCF8574 > >> > datasheet says that minimun level for the High signal must be > >> 0.7*Vdd (so > >> > 0.7*5=3.5V) but the FOX board can generate that level. Ho can it work > ? > >> > > >> > Thanks to everyone for the answers > >> > > >> > Maurizio > >> > > >> > > >> > [Non-text portions of this message have been removed] > >> > > >> > >> I had a very similar question a while ago (see > >> http://tech.groups.yahoo.com/group/foxboard/message/2855). > >> The PCF8574 works between somewhere 2.5V and 6V, so you can just power > >> it with 3.3V too (thanks to Wouter for highlighting this). > >> > >> Best rgds, > >> > >> --Geert > >> > >> > >> > > > > > > [Non-text portions of this message have been removed] > > > > > > > [Non-text portions of this message have been removed]
