Question: In the chip nRF51822, there are 2 crystals 16MHz et 32KHz. I heard that it is possible to put a 32MHz instead of 16MHz? What is the effect on the chip if we place a 32MHz? The 32KHz is for the clock and it is integrated on the chip.

Answer: Yes, it is possible to use a 32 MHz crystal instead of 16 MHz crystal. There is basically no difference between using a 16 or 32 MHz crystal, only a slightly higher current consuption. When using a 32 MHz crystal, the frequency is simply divided by two, so that frequency to be used is 16 MHz. For the 32 kHz clock on the nRF51822, you can either use an external 32 kHz crystal, or the internal RC oscillator. The benefit of using an external 32 kHz crystal is a more accurate crystal and lower current consumption. The start-up time for an external crystal is also shorter than for the RC oscillator. See nRF51822 Product Specification, chapter 8.1.