Power Pins

• 5V: This is the power supply for the module, supply with 3.3-5V power supply input. This will be regulated down to 3.3V to run the chip
• GND: The common/GND pin for power and logic

SPI Pins

• SCK: This is the serial clock pin, by default connected to the Hardware SPI clock pin on the 2x3 ICSP header
• MISO: This is the Microcontroller In Serial Out SPI pin (nRF51 -> Arduino communication) by default connected to the Hardware SPI MISO pin on the 2x3 ICSP header
• MOSI: This is the Microcontroller Out Serial In SPI pin (Arduino -> nRF51 communication) by default connected to the Hardware SPI MOSI pin on the 2x3 ICSP header
• CS: This is the Chip Select SPI pin, which is used to indicate that the SPI device is currently in use. By default connected to digital #8
• IRQ: This is the nRF51 -> Arduino 'interrupt' pin that lets the Arduino or MCU know when data is available on the nRF51, indicating that a new SPI transaction should be initiated by the Arduino/MCU. By default connected to digital #7
• RST: Holding this pin low will put the Bluefruit module into reset. By default connected to digital #4

Other Pins

• SWCLK: This is the SWD clock pin (SWCLK), 3v logic - for advanced hackers!

• SWDIO: This is the SWD data pin (SWDIO), 3v logic - for advanced hackers!

• F.RST: This is the factory reset pin. When all else fails and you did something to really weird out your module, tie this pad to ground while powering up the module and it will factory reset. You should try the DFU reset method first though (see that tutorial page).

• DFU Button: pushing this button when you power the shield up will force the Bluefruit LE module to enter a special firmware update mode to update the firmware over the air.
  Once the device is powered up, this pin can also be used to perform a factory reset. Press the button for >5s until the two LEDs start to blink, then release the pin (set it to 5V or logic high) and a factory reset will be performed.