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,

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.