Datasheet

and then closed. When this happens, the processor will reset, breaking the USB connection to
the computer (meaning that the virtual serial / COM port will disappear). After the processor
resets, the bootloader starts, remaining active for about 8 seconds. The bootloader can also
be initiated by pressing the reset button on the Micro. Note that when the board first powers
up, it will jump straight to the user sketch, if present, rather than initiating the bootloader.
Because of the way the Micro handles reset it's best to let the Arduino software try to initiate
the reset before uploading, especially if you are in the habit of pressing the reset button
before uploading on other boards. If the software can't reset the board you can always start
the bootloader by pressing the reset button on the board.
The Micro has a resettable polyfuse that protects your computer's USB ports from shorts and
overcurrent. Although most computers provide their own internal protection, the fuse
provides an extra layer of protection. If more than 500 mA is applied to the USB port, the
fuse will automatically break the connection until the short or overload is removed.
The maximum length and width of the Micro PCB are 4.8cm and 1.77cm respectively, with
the USB connector extending beyond the former dimension. The layout allows for easy
placement on a solderless breadboard..