Is external crystal neccessary at all on 52832

[Roland]

As i am migrating to 52 and tuning the ble app, i realized by reading many posts here that:

1. external HF xtal is not recommended
2. external LF xtal can be replaced by using internal xtal with temperature compensation.

So does that mean external crystal (either HF or LF ) actually not needed at all on 52?

[Sigurd]

Hi,

1. External HF crystal is mandatory if you want to use the radio peripheral. If you are using BLE, you have to use an external 32 MHz crystal with a frequency tolerance of max 40 ppm. As mentioned in this post:

The external HF clock is critical for data timing and more critical to keep the bluetooth radio on the correct frequency. All the 2.4GHz channels are derived from the 32MHz crystal. So the ppm accuracy of the xtal will be the same ppm accuracy of your carrier in the 2.4GHz band.

2 .

External LF crystal(32 kHz)is not mandatory, but recommend. See this and this post.

Since you are migrating to nRF52832, I recommend to take a look at the General PCB design guidelines for nRF52 series tutorial

[Roland]

@Sigurd,

YES, i have changed the LF src to NRF_CLOCK_LF_SRC_RC. I used 16 for NRF_SDH_CLOCK_LF_RC_CTIV, i will try 32 again.

More facts from my testing:

1. As the application now does not need external LF xtal so i can actually compare the results that same application running on my custom board and the 52DK. on 52DK the application seems all working, as i can discover my services on central side. But just not on custom board.

2. I can not measure 32MHz waveform on my custom board's HF xtal, so apparently it does not work for some reason(though i am not sure for now). But a question is if HF xtal not working is it possible that ble_advertising_start() returned err_code 0? And i can see LED blinking tells that bsp indicator is working.