KL82Z - UART clock accuracy issue with 4MHz internal clock?

[nickbedbury]

I'm using the FRDM-KL82Z eval kit to send bytes from LPUART0 at 115200.    The board is configured to use the 4MHz internal clock.

After testing 10 eval kits, about 50% exhibit framing errors in the UART bytes.  There are no errors if the UART is run at 100000 baud (which happens to be an integer divisor of the 4MHz internal clock...).

We are using Kinetis SDK 1.3.0.

Are there any known issues with the KSDK LPUART software driver related to this?  Or hardware errata perhaps?

[mjbcswitzerland]

Nick

The 4MHz oscillator is a trimmed RC oscillator with a certain amount of tolerance. It may be that the trimming accuracy is varying and so some chips have less accurate baud rates which causes some unreliability, whilst others allow better performance.

In applications requiring reliable UART operation (especially over extended operating range) it makes sense to use a crystal source rather than the RC oscillators, or look into additional factory trimming to achieve a more suitable baud rate result.

Regards

Mark

uTasker developer and supporter (+5'000 hours experience on +60 Kinetis derivatives in +80 product developments)