Crystal accuracy for USB

[john1389]

Posted on July 22, 2016 at 22:58

What ppm accuracy is needed for STM32F103RB as full-speed (12Mbits/s) device?

Is RC HSI (a few percent error) not accurate enough for STM32F103RB as USB device? For STM32F401RE, do host or OTG modes require higher accuracy than device mode?  Does Device 'listen to and derive' clocking speed from Host/OTG and requires less accurate crystal?    #usb-crystal-accuracy

[waclawek.jan]

Posted on July 22, 2016 at 23:11

> Is RC HSI (a few percent error) not accurate enough for STM32F103RB as USB device?

No. From USB2.0, 7.1.11: The full-speed data rate is nominally 12.000 Mb/s. For full-speed only functions, the required data-rate when transmitting (T FDRATE ) is 12.000 Mb/s  ± 0.25% (2,500 ppm). JW