VHDL FF Question

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Hi All,

I am new to VHDL and am attempting to create an object similar to a parallel
load register.  Each FF loads its input from the same signal and all are
clocked by the same signal.  In my "entity" definition I desire only the two
inputs as I don't want to use any more IOB's.  In the architecture block I
declare a signal that is an N-bit vector (say N=8).  However Xilinx ISE 7.1
seems to optimize out the F/F's becuase they are logically not required.
Here is the question; how does one declare a set of F/F's to be instantiated
in "slices" not "IOB's" whose outputs are not used (to be manually routed
later)?

Thanks,

Brendan



Re: VHDL FF Question

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Hallo,

Didnt understand clearly what you are trying to do.Can you post your
entity and architecture to throw some light on it?

Cheers,
Monica,
Germany


Re: VHDL FF Question
On Wed, 4 Jan 2006 09:49:21 -0800, "Brendan Illingworth"

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You can attach an attribute to the signal, (in the architecture part of
the VHDL code) that tells the tools not to optimise it away. Depending
on the synthesis tool you are using, the attribute can have value
"no_opt" or "keep" or "preserve_signal". Check the tool documentation
for details.

- Brian

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