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Adventurer
Adventurer
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Registered: ‎12-16-2008

How to get in Spartan-3 the signal from PAD to internal logic as both non registered and registered in IOB?

I would like to use in Spartan-3 external signal as non registered and at the same time as registered in IOB. I was able to do it in Spartan-3AN as shown in the screenshot. 

In Spartan-3 it refuses to do the same saying that: "Port <xxx> has illegal connections. This port is connected to an input buffer and other components."

Where this limitation comes from? Is it software limitation (ISE14.7) or bug in software? In FPGA Editor I can manually create two path and no DRC are mentioned (see picture).

Any solution for Spartan-3 ?

Manually added non registered path in Spartan-3.jpg
Spartan-3AN IOB.jpg
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Moderator
Moderator
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Registered: ‎04-18-2011

Re: How to get in Spartan-3 the signal from PAD to internal logic as both non registered and registered in IOB?

bit of history lesson for me so I can't say for sure. 

if you look at the FPGA Editor view is the mux path there?

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Adventurer
Adventurer
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Registered: ‎12-16-2008

Re: How to get in Spartan-3 the signal from PAD to internal logic as both non registered and registered in IOB?

First picture shows Spartan-3AN IOB. In addition to IFF I was able to add in FPGA manually unregistered path. But for unknown reasons ISE refuses to do it when running synthesis of the VHDL code (same code works fine in Sparta-3).

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