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.

[Remo]

Just to be sure, you recommend to use the XTAL when using 115200 baud? Because if the RC oscillator of the nRF would have a tolerance of e.g. 4% and the peer device also has a clock tolerance of e.g. 2%, it would not be possible to establish a proper UART communication.

Is it possible that Nordic adds this to the product specification? Because table 8.3 implies that the RC oscillator can be used without any problems for UART communication.

Kind regards