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]>: > > --- In [email protected] <foxboard%40yahoogroups.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]
