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Contributor
Contributor
5,964 Views
Registered: ‎10-20-2010

DCM Reset

 

DCM reset circuit design on virtex5:

 

How many cycles (How long) should we wait once a reset of 3 cycles long is assserted after an unlock has been detected to check whether the DCM is locked or not?

 

 

 

Best regards

iozcelik

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5 Replies
Teacher rcingham
Teacher
5,963 Views
Registered: ‎09-09-2010

Re: DCM Reset

Keep checking until it reported as locked... Simulate it!

Or you could use a PLL, which deasserts its 'locked' output in a more useful manner.

------------------------------------------
"If it don't work in simulation, it won't work on the board."
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Contributor
Contributor
5,962 Views
Registered: ‎10-20-2010

Re: DCM Reset

 

the question is: After a reset, how long does it take for a DCM to get locked under normal conditions.

 

giving another reset too soon will prevent DCM from getting locked. settling time for a DCM is what I wonder.

 

 

 

 

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Instructor
Instructor
5,953 Views
Registered: ‎08-14-2007

Re: DCM Reset

Lock time is specified in the Virtex 5 data sheet (ds202) under the very enlightening title of

"Miscellaneous Timing Parameters."  The maximum lock time depends on the frequency

of the input clock, and also whether you're using the FX outputs or the DLL outputs.  In no

case is it more than 5 ms for DLL or 10 ms for FX outputs.

 

Then to throw a monkey-wrench into the works, they add:

 

Multiplier factor for DLL Lock time with Fine Shift:  2.0

 

So if you use the "fine" shift feature of the DLL you could double the lock time.

 

It is reasonable to assume that these lock times are dependent on the input clock being

stable during the entire locking period.

 

Another word of caution on DCM's:

 

DCM outputs DO NOT TOGGLE while you assert reset!  DON'T USE THE DCM'S OUTPUTS
TO CLOCK THE RESET LOGIC!

 

-- Gabor

-- Gabor
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Contributor
Contributor
5,875 Views
Registered: ‎10-11-2011

Re: DCM Reset

 
Tags (1)
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Teacher eteam00
Teacher
5,871 Views
Registered: ‎07-21-2009

start a new thread!

qd0090,

 

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