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]

Hi Remo,

Sorry for late response. UART will work on 1MHz clock which is generated by dividing 16MHz clock. So the clock jitter of 5% also is divided. With UART it will be maximim of 5% of 1MHz. Now there can also be a clock jitter with the external UART(peer) and if the jitter in the peer is in the opposite direction then it will cause communication issues. I have asked the engineering team to add a note about this in the product specification.

[Remo]

Hi Aryan. This means for us we have to enable the XTAL since our peer devices can also have clock jitter. Thank you for the clarification! A note in the product specification would be great! Kind regards

[Susheel Nuguru]

Sure, I have asked them to add this as a clarification. Can we now close this case?

[Remo]

Of course. I have forgotten to accept the answer.