Hi

I'm trying to connect the mbed and a SAA1064 (7 digit) but I've some trouble with I2c.

I connect resistor between VU (for the 5 volt) and the SDA and SDL but when i put a scope on the line I haven't 5V it is less and different for the 2 wire. And it goes below 0V.

On the SDL the clock is not stable, the impulsion width are not equal.

I don't know what to do.

The mbed works with 3v3. It's better to work with a level converter when connecting 3v3 I2C and 5V I2C lines. If the signals go below 0V, please check the ground wire.

Hello,

you must use the same voltage as the mbed voltage even in pull-up resistors so you must use Vdd = 3v3.

This photo is the general configuration circuit for I2C:

This photo is a special configuration when using multiple voltage at the same system (Level Shifter):

also check this link in NXP website about I2C: http://www.nxp.com/news/backgrounders/bg_esc9727/

Have a nice day

Have a look at this document... http://www.nxp.com/documents/application_note/AN10441.pdf

Thx for the rapid answer

So the mbed works with 3.3 and the SAA1064 in 5V and i must ad the 2 MOS to make the connection possible.

Which MOS I have to use?

The BSN10 or BSN20 can be used as MOS FET. Almost the same doc ( also NXP ) See page 13.

http://ics.nxp.com/support/documents/interface/pdf/an97055.pdf

Thx a lot for your help i will test that tomorrow and post a message after. I hope it will be good.

yes Ben thats right Philips BSN10 and BSN20 MOSFETs are all suitable for this level-shifting function in addition to BSS83