Announcement

Collapse
No announcement yet.

I2C voltage

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • I2C voltage

    Hi
    what's the correct voltage to apply to I2C lines on a uLCD32 ? can I use it at 5V or it's best to work at 3.3V ? thanks
    Giampaolo

  • #2


    Although the I2C pins of the Picaso chip are open drain and will allow pullups to 5v,
    there is already pullups on the PCB to 3v3 so it is recommended to use 3v3 I2C devices although many
    5v devices will work well with 3v3 SDA and SCL lines.
    Have a look at the specs of the device(s) you wish to use.
    Regards,
    Dave

    Comment


    • #3


      Hello Dave
      thanks a lot for your support...
      are you sure there are pullups resistors to 3.3V ? there are no ones in the schematics... and without external ones my I2C chain wasn't even move SDA/SCL signals on the oscilloscope...
      also... I'll suggest 4D guys to specify in the user docs that I2C is supposed to work with 3.3V devices... I found something in an old post but nothing in the official manuals.
      thanks again
      Giampaolo

      Comment


      • #4


        Pullups resistors to 3.3V are on P1-EB shield.
        Thierry - Avignon - France
        Regards,

        Thierry - Avignon - France

        Comment


        • #5


          Herro Thierry
          sorry... I don't understand what do you mean... what's P1-EB ? do you mean BUS0-7 or GPIO1-5 ? thanks a lot Giampaolo

          Comment


          • #6


            It's the expansion board -> http://www.4dsystems.com.au/prod.php?id=69
            Regards,

            Thierry - Avignon - France

            Comment


            • #7


              Hello Thierry
              thanks! it's all clear now!
              Best Regards from Italy,
              Giampaolo

              Comment


              • #8


                Yes apologies Giampaolo, there are no pullups on the earlier PCB's - they were catered for on the expansion board and are coupled to 3v3.

                Although the docs do mention that generally, pins are 5.0V tolerant they do not mention the I2C pins specifically. The docs will be updated accordingly.
                Regards,
                Dave

                Comment


                • #9


                  Hi there,
                  could you be more more specific. For instance the DS1307 RTC which is a 5V device, is it possible to hook it up to my uLCD32 or not?

                  Thanks

                  stenhh

                  Comment


                  • #10


                    I think no, I use DS1340-C RTC with my 4D module and it works well.Usualy, all I2C slave device accept both 3.3V and 5 V. For I2C master ┬Áp, you must chose I2C (5V) or SMB (3.3V) bus type.
                    Regards,

                    Thierry - Avignon - France

                    Comment

                    Working...
                    X