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A new design will not enumerate.

Last Updated: September 26, 2011

A new design on EZ-USB will not enumerate. What are the things to be checked?


For a custom board, look first at the following signals:


  • XIN  -   is there an oscillation on this signal?
    If no, check crystal specs and layout

  • Vcc on all power input pins (see TRM for pins)


  • AVcc for at least 3.0 volts and no greater than 3.6 volts
  • Insure there is a 1.5K ohm resistor connected to the D+ USB connector pin 3 and that it is controlled to signal the host that a device has connected.


  • The matching series resistor on both the D+ and D- lines from the USB connector to the EZUSB chip.  This value is selected for signal quality and is normally in the range of 22 to 30 ohms.



  • That the reset signal is in the range of 7 to 10 msec.  This period is measured from the start of valid power.



  • Pins TEST, TM0, TM1, C24TST and C48TST are tied according to the manual.



  • SCL and SDA have valid pull ups  (2.2K to 10 K ohms)

    For firmware loaded onto our development board, try enumeration without EEPROM so the SIE controls the VID/PID. If problems persist, please open a support case for additional assistance.

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