Re: [usb] question about the DLL in the UTMI

[Rudolf Usselmann <rudi@asics.ws>]

On Tuesday 18 September 2001 10:16, you wrote:
> Hi,everyone:
>
>     I have some questions about UTMI. Can someone help me?
> Thank you.
>
>   I saw a module with the name of "FS DLL & Data Recover"
> in the figure2: UTM Function Block Diagram . I don't know
> the exact function of that module. The explanation in the
> UTMI Spec. is that:
>
> 5.2 HS DLL (High Speed Delay Line PLL)
> The delay line PLL extracts clock and data from the data received
> over the USB 2.0 interface for reception by the Receive Deserializer.
> A vendor defined number of delayed clock taps are be used to sample the
> received data. The data output from the DLL is synchronous with the local
> clock.
>
> My question is :
> How about the relation between the clock extracted from the the data
> received over the USB2.0 interface and the local clock ?  Why to exact
> clock from the received data?  Which clock is used to sample the recieved
> data, the exact clock or local clock from the local Clock Multiplier ?

Well, you extract first the RX clock from the received data stream
and based on that extract the data. Than you perform serial to
parallel conversion (including bit-unstuffing). Then you place the
data in to an internal FIFO. The output from the FIFO is synchronized
to the local clock. Typically you would have a 480 MHz bit clock, and
a 60 MHz "local" clock which is the UTMI interface clock. The 60 MHz
are derived by presenting 8 bits at a time (480/8=60). There is also
a 16 bit version of the UTMI interface, that runs at 30 MHz ...


>  What is the meaning of "Delay Line"? is it refer to the delayed clock
> taps of vendor defined ? I was so puzzled about DLL.

A DLL is digital PLL. There is an white paper on www.usb.org.

> Thanks.
> Best Regards.

rudi
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