ColdFire/68K Microcontrollers and Processors中的主题 Re: Clock source for USB on MCF52223

Clock source for USB on MCF52223

Hjerrild — Tue, 14 Nov 2006 23:12:25 GMT

Hi, I'm a bit confused about how to USB device in the MCF52223 should be clocked.

What clock frequency should the USB device have? Is it connected to the clock tree like all the other internal devices or is it getting the clock directly from oscilator block?

In the MCF52223 Reference Manual Rev. 2 Figure 5-1 the USB device is not shown. Is that an error? Is the FlexCAN device replaced with USB??

Best Regards Hjerrild

Re: Clock source for USB on MCF52223

DrSeuss — Wed, 15 Nov 2006 03:00:48 GMT

The USB modual can be clocked directly from the 48 MHz external crystal or from the USB_ALT_CLK pin. It is not quite acurate to replace the CAN in the figure 5-1. There is No CAN on the mcf52223, I will correct.

Re: Clock source for USB on MCF52223

giga — Tue, 06 Mar 2007 04:11:48 GMT

Is there an updated clock tree showing the USB module? I am looking at Rev. 2 of the reference manual. Also, I don't see in the data sheet where it references the USB_ALT_CLK in the pin functions as any of the primary, secondary or tertiary functions, however I do see it referenced on the demo board schematic and the USB_CTRL register. I am trying to figure out how to drive the USB from the PLL with an 8MHz input, 80MHz core clock and 48MHz USB clock. Is that possible?