baud rate change when usb plugin computer

RE: baud rate change when usb plugin computer

ovrebekk — Fri, 09 Aug 2019 10:12:30 GMT

Hi Brian

When using the SoftDevice you should request external HF clock through the sd_clock_hfclk_request() function.

Best regards
Torbjørn

RE: baud rate change when usb plugin computer

yqin15 — Fri, 09 Aug 2019 01:38:47 GMT

Hi Torbjørn:

Thanks for quick response,

yes I use sd140 with sdk 15.2, please advise how to manually request external HF clock for uart? thanks

Brian Qin.

RE: baud rate change when usb plugin computer

ovrebekk — Thu, 08 Aug 2019 13:38:57 GMT

Hi Brian

To get stable baudrate when using the UART it is important to use the external HF crystal. The internal HF source can deviate by as much as 8%, and the internal source is the default unless the external one is requested by software.

Most likely the USB driver will request this when the USB is running, which is why the USB connection affects the accuracy.

Can you try to request external HF clock manually and see if it improves the accuracy?

If you need advice on how to do this please let me know if you use a Bluetooth SoftDevice or not, as the method for requesting external HF clock differs when using it.

Best regards
Torbjørn

RE: baud rate change when usb plugin computer

yqin15 — Thu, 08 Aug 2019 11:28:56 GMT

more information: when pulg usb into a 5 v power supplier instead of usb port of pc, the baudrate is same as not plugin, and it seems a little tremble than plugin to usb of a pc, when plug in pc, the baudrate is more stable,