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. Although most computers provide their own internal protection, the fuse provides an extra layer of protection. The Mega 2560 has a resettable polyfuse that protects your computer's USB ports from shorts and overcurrent. See this user-contributed tutorial for more information. Or you can use the ISP header with an external programmer (overwriting the DFU bootloader). You can then use Atmel's FLIP software (Windows) or the DFU programmer (Mac OS X and Linux) to load a new firmware.
![arduino mega 2560 pinout arduino mega 2560 pinout](http://somanybits.com/images/forum/Pin%20Arduino%20Mega%202660.jpg)
The Mega 2560 is an update to the Arduino Mega, which it replaces.
![arduino mega 2560 pinout arduino mega 2560 pinout](https://europe1.discourse-cdn.com/arduino/original/4X/f/6/2/f6258a2ebd00a3f75099715f82914ed17175130f.jpeg)
The Mega 2560 board is compatible with most shields designed for the Uno and the former boards Duemilanove or Diecimila. It contains everything needed to support the microcontroller simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. It has 54 digital input/output pins (of which 15 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. The Arduino Mega 2560 is a microcontroller board based on the ATmega2560.