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Contributor
Contributor
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Registered: ‎09-07-2014

CARRY4 Direct Instantiation

Hello,

 

According to Fig2-24 in ug474 the CARRY4 unit has two inputs, CI and CYINIT, that connected directly to internal multiplexer that selects which input will be used as the first carry-bit (c0) of the chain.

In order to implement a cascaded CARRY4 chain, I want to instantiate multiple CARRY4 primitives directly.

However, the 7-series libraries (ug953) description for the CARRY4 does not contain any information how to direct the CARRY4 unit which carry input should be used. Moreover, the CARRY4 unit shown in the Device viewer in Vivado tool does not include any kind of such internal multiplexer, and the CI input is simply left unconnected!

My questions are:

1) Which of the descriptions above (vivado viewer vs. ug474) is the correct?

2) How should I managed direct CARRY4 instantiation?

 

Please advise.

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