Re: More basic questions about Spartan 2 IOB

>In the Spartan 2 datasheet I read:
>'The IOB includes an optional register in the output path,
>the input path, and the 3 state control pin.
>
>In the diagram this is clear.
>
>Questions arise:
>Can the 3 state register be controlled independently?

What do you mean by "independently"?  Look at the diagram.
Are the clocks shared?  Are separate clock enables good
enough for your application?


>So what are the exact commands for the UCF file to:
>Switch off / on the input register.
>Select a pos or neg clock for the input and output registers.
>What are the defaults?

The usual approach is that your code or schematics makes the registers
and tri-state buffer, and then you place them in the IOB (if that's
where you want them).

There are probably convenient library elements that may help you
easily get what you want.  You probably want to find the library
documentation anyway - lots of good ideas in there, especially
for the details like you are asking about.

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