Power Pins

• VIN: This is the power supply for the module, supply with 3.3-16V 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, connected to SCK on your Arduino or MCU
• MISO: This is the Microcontroller In Serial Out SPI pin (nRF51 -> Arduino communication)
• MOSI: This is the Microcontroller Out Serial In SPI pin (Arduino -> nRF51 communication)
• CS: This is the Chip Select SPI pin, which is used to indicate that the SPI device is currently in use.
• 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.

Other Pins

• DFU: Setting this pin low when you power the device 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.  Wire the pin to GND 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.
• RST: Holding this pin low then releasing it (or wiring it HIGH) will cause a system reset

Reverse Side Breakouts

On the back we also have a few breakouts!

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

DIO: 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).

3.3V: This is the output from the 3V regulator, for testing and also if you really need regulated 3V, up to 250mA available