On May 3, 2011, at 4:16 PM, V G wrote:

> 2. Does the LUT itself provide the logic functionality? As in AND, =20
> OR, XOR,
> NOT, whatever gates? If so, where are the inputs to the gates, and =20
> what are
> the LUT inputs for?
>
> 3. What kind of "function" can LUTs provide?

a LUT provides a logical output capable of computing ANY logical =20
equation based on its inputs.
Given three inputs, there are only 8 possible outputs.  I think of a =20
LUT as an array of bits, addressed by the inputs.  You get to specify =20
the array contents (and thus the logic function) as part of the device =20
programming.  On many devices, the LUT may actually be implemented as =20
a RAM array of bits, but I don't think that that is actually required. =20
Other implementations are possible.

So if you wanted to implement an AND function, your 3-bit LUT would =20
have zeros in all the table locations except the one corresponding to =20
1 1 1 inputs.

BillW


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