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Atmel Micro does not load EEPROM data

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  • Atmel Micro does not load EEPROM data


    I am using the micro-USB with a controller that uses the Atmel Mega2561. If I have the USB cable plugged into the PC and the micro-USB before I power the controller, the EEPROM data is not loaded into the Mega2561.

    If the controller is power first I do not have this problem. I have the Tx and Rx on the mirco-USB and Mega2561 directly connected. As far as transferring data in both directions it works perfectly.

    My question is should I have some component in the Tx and Rx lines. Or is there something else I should be doing to stop this.

    Ray Hall.

  • #2


    How have you got it setup? Are you powering the controller via the uUSB or a separate supply? Which micro-USB module is it...uUSB, uUSB-MB5, uUSB-CE5 ? If you are powering up your target app via the micro-USB are you using the 5V or the 3.3V supply? Please supply more detail of your configuration.


    • #3

      I am using the µUSB

      The controller is powered by its own internal power supply. The 5volt and 3.3 volt supply on the micro-USB are not used or connected in any way. Only connections are Tx, Rx and Gnd.



      • #4


        You've probably already done this, but two things that I tend to look for when I'm having trouble interfacing to a uController are:

        1. Are the Grounds on the uUSB and the host power supply tied together?

        2. Are you using pullup resistors (I normally use 10K) on the Rx & Tx lines. Some hosts don't like their Rx lines to "float" during power up. It's usually more important to have the pullup on the host Rx line.

        Good luck,

        Any technology, sufficiently developed, is indistinguishable from magic. A.C. Clark(RIP)

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        • #5


          I connected a 10k resistor from the uUSB 5v supply pin to the Tx pin (Rx on Mega2561) and it solved the problem.

          Thank you very much.