Member Since: April 20, 2011

Country: United States

  • I just found that crackmonkey commented with an equivalent fix on the Fio v3 product page.

  • Here’s the fix. Unfortunately it has to be made in the Arduino core code.

    In the USBDevice_::attach() function of arduino-1.0.1\hardware\arduino\cores\arduino\USBcore.cpp, line 641, change:

    PLLCSR = 0x12;          // Need 16 MHz xtal

    to this:

    PLLCSR = 0x12;          // Need 16 MHz xtal
    #if (F_CPU == 8000000)
        PLLCSR = 0x02;          // Alternately, support 8MHz

    Bit 4 of the PLLCSR register enables a divide-by-2 of the input clock to the PLL. This is needed for a 16 MHz design, but should not be enabled for an 8 MHz clock.

    If you select the SparkFun Pro Micro 3.3V/8MHz board type when compiling your sketches, then the F_CPU define will already be set to 8000000 for you.

    After making this change, the example sketches provided by Arduino 1.0.1 were able to enumerate as both a CDC serial port and HID device.

  • Has anyone had this 8 MHz Pro Micro work as the multi-function USB device (CDC and HID) provided with Arduino 1.0.1?

    I have a similar design with an 8MHz clock and used this board as a reference. I knew I would have to rebuild the bootloader to support the 8MHz clock - that was easy, just change the F_CPU frequency definition in the Caterina bootloader Makefile.

    But once I put a sketch into the Arduino, Windows could not identify the device. None of the basic example sketches could be enumerated by Windows, it was always complaining about an “unknown device.”

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