16MHz RC oscillator accurate enough for UART

[Remo]

Hi all

According the nRF51822 Product Specification V3.1, the 16MHz RC oscillator has a tolerance of at most 5% and can be used as clock source for the UART module.

Due to several sources on the internet, the maximum tolerance for a proper UART communication is 4%. This would give 2% to the transmitter and 2% to the receiver.

Therefore, is the RC oscillator really accurate enough? Am I missing something?

Kind regards

Remo

[Susheel Nuguru]

When using RC oscillator, if you are using hardware flow control, then i have not seen any issues even using high baudrate. But if you are not using hardware flow control then there can be framing errors with baudrate starting 38400.

It is highly recommended to use XTAL when not using flow control.

[Susheel Nuguru]

Hi Remo,

You have a point, that the jitter on the RC clock should not have anything to do with flow control. Like I said, this was my experience when using high baudrates. This is not documented anywhere. The highest I tried was 115200. If you do not want to use XTAL and want to use 115200 baud, then make sure that your software handles framing errors.

correct, softdevice will not explicitly turnoff the XTAL if you use sd_clock_hfclk_request().