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Adventurer
Adventurer
3,072 Views
Registered: ‎02-13-2013

carry4

Hi,

 

I'm using the CARRY4 as a delay line for a signal. I have the following code..

 

cmp_carry:CARRY4 port map(
     CO => delay(3 downto 0),
     CI => '0',
     CYINIT => start,
     DI => "0000",
     S => "1111"
);

 

Now, I need to know how the CO pass to delay, I mind, for example

 

               CO(0) => delay(0)

               CO(1) => delay(1)

               CO(2) => delay(2)

               CO(3) => delay(3)

 

Or in this way

 

               CO(0) => delay(3)

               CO(1) => delay(2)

               CO(2) => delay(1)

               CO(3) => delay(0)

 

Can anybody help me?

 

Regards

 

 

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2 Replies
Instructor
Instructor
3,065 Views
Registered: ‎08-14-2007

Re: carry4

The Libraries Guide for Spartan 6 shows the ports numbered CO(3:0) which implies

that your first connection would be correct.  However before you go too far down that

path, you should know that the CARRY4 of a Spartan 6 includes lookahead logic and

may not really be represented as shown in the diagram.  i.e.  the delay to output CO(0)

through CO(3) may not rise monotonically.

 

Also if you are doing anything with the output other than routing it to the adjacent

flip-flop, routing delays will be significantly greater than the propagation through

the carry chain.

-- Gabor
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Highlighted
Observer a.turowski
Observer
2,522 Views
Registered: ‎10-26-2012

Re: carry4

Hi lalobegar,

 

Did you get anywhere with using CARRY4 as a delay line? Is the delay on CO outputs monotonic?

 

Best regards,

Adam

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