Accurate or custom baudrate on nrf9160

[Chraebs]

Hi

On a nrf9160, I need to send data via UART(E) at 921600 baud. According to the UARTE BAUDRATE register documentation the register value 0xF000000 (Baud921600) leads to an actual rate of 941176 Hz. This is also what I measure on the oscilloscope. Setting the BAUDRATE register to an interpolated value 0xEBEDFA4 seems to result still in approx. 940000. What is the recommended way to achieve more accurate baudrate 921600?

Follow-up question: Is it possible to use custom baud rates, or are only the baudrates listed in the UARTE BAUDRATE register documentation supported?

Thanks,
Matthias

[vkadal]

Custom baud rate can be used, provided both the devices has the same buad rate. Even small change in the clock will result in error.  So you shall us cristal clock to have effective communication

[Chraebs]

Here are some measurement results on a nrf9160dk. I assume the non-linearity at high baudrates is due to timer multiplications?

REGISTER       Measurement
0x06000000 --> 380000 baud
0x0F000000 --> 940000 baud
0x0EAFC293 --> 939000 baud
0x0E679E98 --> 939000 baud
0x0A000000 --> 638500 baud
0x0D000000 --> 849600 baud
0x0E100000 --> 893000 baud (double checked. This is higher than for 0x0E200000 !!)
0x0E200000 --> 878000 baud
0x0E300000 --> 878000 baud
0x0E400000 --> 939800 baud