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Newbie anatolich
Newbie
5,837 Views
Registered: ‎10-10-2011

Two parallel DCMs on Spartan3e

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Using two DCMs. If it is used two different pins - everything is fine. But it is not posible to use one input on one pin for both DCMs. Is it possible in principle to use an one pin for all DCMs on chip.
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Instructor
Instructor
8,100 Views
Registered: ‎08-14-2007

Re: Two parallel DCMs on Spartan3e

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You could theoretically use all the DCM's from a single pin.  However you may need to

use the CLOCK_DEDICATED_ROUTE constraint to allow the pin to route to the DCM's

on the other side of the chip.

 

Usually the problem with using two DCM's from a single clock input pin is that the

clock input buffer gets duplicated, leading to map errors (cannot place these two

IBUFG components in this one IOB).  If you use the clock architecture wizard you

need to select "internal" as the DCM input source, and explicitly instantiate the

IBUFG at the top level of your project, using the output of the IBUFG component

to drive all of your DCM's

 

-- Gabor

-- Gabor
2 Replies
Instructor
Instructor
8,101 Views
Registered: ‎08-14-2007

Re: Two parallel DCMs on Spartan3e

Jump to solution

You could theoretically use all the DCM's from a single pin.  However you may need to

use the CLOCK_DEDICATED_ROUTE constraint to allow the pin to route to the DCM's

on the other side of the chip.

 

Usually the problem with using two DCM's from a single clock input pin is that the

clock input buffer gets duplicated, leading to map errors (cannot place these two

IBUFG components in this one IOB).  If you use the clock architecture wizard you

need to select "internal" as the DCM input source, and explicitly instantiate the

IBUFG at the top level of your project, using the output of the IBUFG component

to drive all of your DCM's

 

-- Gabor

-- Gabor
Xilinx Employee
Xilinx Employee
5,800 Views
Registered: ‎06-30-2010

Re: Two parallel DCMs on Spartan3e

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You can drive multiple DCMs from one input and as Gabor said you will need to ensure that you set the input to "Internal" in the wizard and manually instantiate an IBUFG.

 

There are restrictions on which DCMs can be driven from what GCLK pins, this is illustrated on page 47 of UG331: http://www.xilinx.com/support/documentation/user_guides/ug331.pdf 

 

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