add a bus driver between pcf8574 and lcd then
Quoting maurizio bertero <[EMAIL PROTECTED]>: > 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] > >
