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Explorer
Explorer
13,111 Views
Registered: ‎08-07-2013

Spartan-6 Clock generator

 

Hi,

 

Are there any clock management module like DCM in Spartan-6?  How to handle

a clock in Spartan-6?

 

Regards,

 

 

Peter

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19 Replies
Xilinx Employee
Xilinx Employee
13,109 Views
Registered: ‎09-20-2012

Re: Spartan-6 Clock generator

Hi,

 

DCM is available in Spartan-6. It can be instantiated using primitives DCM_SP or DCM_CLKGEN. Refer to http://www.xilinx.com/support/documentation/user_guides/ug382.pdf for more details.

 

If this does not address your query please elobarate it.

 

Thanks,

Deepika.

Thanks,
Deepika.
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Historian
Historian
13,094 Views
Registered: ‎02-25-2008

Re: Spartan-6 Clock generator


@peterchang0708 wrote:

 

Are there any clock management module like DCM in Spartan-6?  How to handle

a clock in Spartan-6?


Ya know, if you'd bothered to spend thirty seconds looking at the Spartan-6 Family Overview document, you would have seen the section titled "Clock Management."

----------------------------Yes, I do this for a living.
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Explorer
Explorer
13,047 Views
Registered: ‎08-07-2013

Re: Spartan-6 Clock generator

 

One further question.

Can I use a DCM generated based on a device Spartan-3 from coregen, and used in a Spartan-6 device?

Thanks.

 

Peter

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Teacher eteam00
Teacher
13,041 Views
Registered: ‎07-21-2009

Re: Spartan-6 Clock generator

No.  Re-generate the DCM instantiation using the Spartan-6 Clock Wizard.  This is a 2-minute task.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
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Explorer
Explorer
13,026 Views
Registered: ‎08-07-2013

Re: Spartan-6 Clock generator

Many thanks.

 

Peter

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Explorer
Explorer
13,010 Views
Registered: ‎08-07-2013

Re: Spartan-6 Clock generator

 

Hi Bob,

 

Another problem I have about the DCM is that, though it is easy to generate a DCM, I don't know why the performace

isn't well according to my experience.  Let me give you an example.  I've try to generate a DCM wtih one 27Mhz input,

3 outputs, 27Mhz, 54Mhz, and 74.25Mhz.  All have 50% duty.  And generated by auto mode, which is supposed to

be a PLL based DCM.  The result I saw on the scope isn't so well for the 74.25Mhz clock.  It is about 71 ~ 72Mhz.

Sometimes, 76Mhz.  Not so stable.  And the duty isn't so good either.  Why?  Are there any way to improve the

performance.  Many thanks.

 

 

Peter

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Xilinx Employee
Xilinx Employee
13,003 Views
Registered: ‎01-03-2008

Re: Spartan-6 Clock generator

The problem is likely with your scope having a bandwidth that is too low. Is it at least a 300 MHz scope?
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Teacher eteam00
Teacher
13,000 Views
Registered: ‎07-21-2009

Re: Spartan-6 Clock generator

It sounds like you are working with digital video, based on the clock frequencies you mention.

 

Start with your clock source.

 

  • What is the clock source?
  • Is the clock source stable?  How is the source clock generated?
  • Is the clock source constantly running, or does it drop out with (for example) switched connections?

 

Next is your DCM instantiation.  Please post your code for this.

 

Finally, how are you measuring the clock frequencies?  What instruments are you using, and how accurate are they?  You need a 300MHz scope (as McGett writes) for an accurate display of the *shape* of the clock, but you do not need a 300MHz scope to measure the frequency of a 27MHz clock.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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Explorer
Explorer
12,992 Views
Registered: ‎08-07-2013

Re: Spartan-6 Clock generator

 

Hi Bob,

 

You got it.  You must be familiar with it.  Let me explain more as below.

 

Input clock source; OSC 27Mhz, (measurement on scope; period:37ns, freq.: 27.027, duty: 44.61%) stable.

FPGA: Spartan-6  XC6SLX150, FGG676 ( xc6slx150-2fgg676, for the speed grade, I select -2)

DCM is generated in auot by coregen as the attached file.

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Explorer
Explorer
9,277 Views
Registered: ‎08-07-2013

Re: Spartan-6 Clock generator

 

Hi ,

 

Scope is Agilent 500Mhz Mixed Signal Oscilloscope

MSO6054A

Suppose, it is okay.

 

 

Peter

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Explorer
Explorer
9,277 Views
Registered: ‎08-07-2013

Re: Spartan-6 Clock generator

Hi Bob,

 

The scope is Agilent 500Mhz Mixed Signal Oscilloscope

MSO6054A

Suppose, it is okay for the measurement.

 

Peter

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Teacher eteam00
Teacher
9,257 Views
Registered: ‎07-21-2009

Re: Spartan-6 Clock generator

Suggest you try using a PLL instead of a DCM.  Report back with your results when you are ready.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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Explorer
Explorer
9,245 Views
Registered: ‎08-07-2013

Re: Spartan-6 Clock generator

 

 

Hi Bob,

 

The clock of 74.25 becomes

 

         ..............             ..............            ........

.........|             |............|             |............|

             7ns       6ns         7ns      6ns

 

much better.  But still not stable, some clocks will

not in phase, for example.

 

 

      ........           ................                  ........

......|       |..........|               |..................|       |...

       4ns   5.1ns    7.9ns        9.1ns

 

       | <----        26.1 ns   -------------->|                    

 

From two of those clock, the frequency may about the same, but much different

for each.

 

 

 

Peter

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Teacher eteam00
Teacher
9,231 Views
Registered: ‎07-21-2009

Re: Spartan-6 Clock generator

Please understand that I cannot look over your shoulder and see what you are seeing.  These are tet messages in an online forum, not a classroom discussion room.  You MUST communicate as clearly and concisely as possible.

 

 But still not stable, some clocks will not in phase

 

What does this mean?  Which clocks are not 'in phase' ?  What does 'in phase' mean?
Do you expect 74.25MHz clocks and 27MHz clocks will be in phase with each other?

 

I have never seen PLL-generated outputs with oddly non-uniform pulse widths as you have illustrated.  Please clarify how these clock waveforms were generated, how these waveforms were measured, and please attach code snippets where your clocks are generated (DCM and PLL instantiations).

 

Thank you.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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Explorer
Explorer
9,206 Views
Registered: ‎08-07-2013

Re: Spartan-6 Clock generator

 

 

Dear Bob,

 

Thanks for your help.  The clock is now getting better after adding some contraints by contraint editor.

Many thanks.

 

 

 

Peter

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Xilinx Employee
Xilinx Employee
9,201 Views
Registered: ‎08-01-2012

Re: Spartan-6 Clock generator

One more thing you have to verify 'Requested' and  'Actual' values while generating DCM clocks in Coregen tools.Due to Multiply (M) & Divide (D) combinations difficulty some times the DCM may not generate exact requested values.They gennerated nerest possible values will be shown in "Actual" values while genrating DCM core.

 

If the above is not issue then it may be osciloscope probe bandwidth problem.

 

 

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

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Explorer
Explorer
9,182 Views
Registered: ‎08-07-2013

Re: Spartan-6 Clock generator

Hi Kodali,

 

Thanks for your further comment.  Yes, you're right.  The scope is 500Mhz.  And the probe is the original.

Supposed, both are okay for the measurement.  DCM is able to generate a close value.  Not exactly, as

far as I know, for the case.  Right now, the freq.  I've gotten is acceptable.

 

 

 

Peter

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Scholar joelby
Scholar
9,163 Views
Registered: ‎10-05-2010

Re: Spartan-6 Clock generator

How are you outputting the clocks to FPGA pins for observation? Are you using ODDR2?

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Xilinx Employee
Xilinx Employee
9,149 Views
Registered: ‎08-01-2012

Re: Spartan-6 Clock generator

No. You can not use a DCM generated based on a device Spartan-3 from coregen,to Spartan-6 device. You have to generate seperate DCM for Spartan-6

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