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I2C Fm+ Newbie

Former Member

I'm starting to work on a board that will use mostly I2C Fm+ devices, does anyone have any hints or tricks that caught them off guard when working with these devices at the 1MHz bus speed?  I'm particularity interested in board layout, bus capacitance, etc. but any other input would be great!

  • No special hints or tricks but do make sure to read the NXP spec (easily found by Googling I2C Fm+).

    Apologies if you have already read it, but I'm frequently amazed by designers who try to implement I2C without reading the real spec first.

     

    Of course you need to study the chip data sheets too to spot all those little wrinkles where they have "improved" upon the spec image

     

    MK

  • in reply to michaelkellett

    Thanks MK these I have skimmed over and will do the work that I should do in reading.  I'm sure once I get into it I will find out more, I just don't want to fall into any "common" mistakes that designers make, other than not reading the real spec :-D  Thanks again

  • in reply to Former Member

    Hello Jason, which chips are you using - I'm quite interested in I2C Fm so it's nice to know which parts others are using.

     

    Thanks.

     

    MK

  • in reply to michaelkellett

    My list includes:

     

    Mfg:               Mfg#:                                        Description:

    TI                   DAC5571IDBVT                         DAC 8-Bit 188KSPS I2C TSOT-23-

    Microchip       MCP23018-E/MJ                       I/O EXPANDER I2C 16-Bit 24QFN

    On Semi        CAT24M01WI-GT3                     EEPROM 1MBIT 1MHZ 8SOIC

    NXP               PCF8523T/1,118                       RTC CALENDAR 8SOIC

    TI                  TMP101NA/3K                           DIGITAL TEMP SENSOR

    On Semi        NCD9830DBR2G                       ADC 8-BIT 8-CH I2C 70KSPS

    Honeywell      HMC5883L                                COMPASS 3 AXIS 16-LCC

     

    These are the devices I'm looking closely at, they are all Fm+ or HS devices, and I want to be able to put them all on the same bus and run at the full 1MHz.

     

    I have a few more questions: Lets say I decided to have a mixed speed bus with Fm+ and Fm devices with on master, is it up to the master to know which devices are Fm and Fm+? Also is it up to the master to control the speed at which it communicates to the devices?  Finally when communicating to higher speed devices how does a lower speed device deal with the higher speed traffic?