Datasheet

V850ES/JG3-H, V850ES/JH3-H CHAPTER 21 USB FUNCTION CONTROLLER (USBF)
R01UH0042EJ0500 Rev.5.00 Page 1049 of 1513
Aug 12, 2011
21.4 Cautions
(1) Clock accuracy
To operate the USB function controller, the internal clock (6 MHz external clock × internal clock multiplied by 8 = 48
MHz internal clock) or external clock (external clock input to UCLK pin (f
USB = 48 MHz)) must be used as the USB
clock. When the internal clock is used as the USB clock, use a resonator with an accuracy of 6 MHz ±500 ppm
(max.). When the external clock is used, apply a clock with an accuracy of 48 MHz ±500 ppm (max.) to the UCLK
pin. If the USB clock accuracy drops, the transmission data cannot satisfy the USB rating.
(2) Stopping the USB clock
When the main clock (f
XX) has been selected as the USB function controller clock and it is necessary to stop the
USB function controller, be sure to stop the USB function controller (by setting bits 1 and 0 of the UFCKMSK
register to 1) first before stopping the main clock (f
XX).
If the main clock (fXX) is stopped without first stopping the USB function controller, a malfunction might occur due to
noise in the clock pulse when the main clock (f
XX) is restarted.
Similarly, when an external clock whose signal is input from the EXCLK pin is selected as the USB function
controller clock, measures must be taken to prevent noise from being generated in the clock pulse by the external
circuit. If this is not feasible, then the USB function controller must be stopped first before stopping the main clock
(f
XX).