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

["Luis J. Perez" <luis.perez@ds2.es>]

Hello Jiang daosan,

I think that the named "local clock" is the external clock you need to
generate the "extracted clock", and also used as CLK OUT to the USB
Device controller. So, the extracted clock is a 12 MHz or 480 MHz (FS or
HS) clock generated from the external clock (divide it!).
To design a HS PLL you need an external clock of 480x4 MHz (at least, I
think) to obtain the data signal synchronized with the internally
extracted 480 MHz clock.

The need of extracting the clock from the received data is to syncronize
it with the incoming clock from the HOST/HUB controller.

The clock used to sample the received data is the external (30, 48, 60
MHz, it depends on you..., and your design).

About the term "delay line", as you need to sample the received data and
generate the internal clock, the output data from the DPLL will be
delayed from the incoming data from the USB wire.

Well, I also WAS puzzled with DLL a month ago, and I've learned a lot
from the people in this list.

I wish my answers (if no mistake: please, correct me if I'm confused)
will solve your doubts...

Regards,

  --- Luis ---


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


========================================================
Luis Jose Perez Lafuente      	luis.perez@ds2.es
Design Engineer
Digital Design Department

Design of Systems on Silicon  	http://www.ds2.es
Av. Charles Robert Darwin, 2  	Phone.  +34-96-136 60 04
Parc Tecnologic	              	                Ext. 152
46980 Paterna (VALENCIA)      	FAX     +34-96-136 62 50
SPAIN
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