Re: two questions

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This is not a question... :)

Equality compares are easy.  It uses a two input XOR for each bit with
all the results being OR'd together.  This will take 32 LUTs for the XOR
and the first OR gate and 11 more LUTs to combine the rest for a total
of 43 LUTs in four levels.  If the design uses the "special" features
that most chips have (ORing of LUTs within a CLB), you can use the LUTs
in pairs or even groups of four and reduce the number of levels for
speed.  


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Is that 16 bit address (64k words) of 8 bit words?  Because 64k x 8 =
512K.  

You can get this much RAM in the VirtexII if you use the XC2V500 part.
Or in the new Spartan3 you could use a XC3S1500.  I am not sure which
will be cheaper, but I bet it is the Spartan3.  

The speed of the block RAM will be much faster than anything external to
the FPGA.  The block ram will be synchronous and lends itself well to
pipelined operations.  

A lot of how you design will be implemented will depend on your data
flow which you have said nothing about.  Think about how the storage
will be orgainized and accessed.  Obviously one large block of memory
with one interface will not let you do 64 compares at one time.  If you
rate of performing these compares is not fast, you can use one compare
logic block and run the different data through it sequentially.  Then
one memory could easily do the job.  

--

Rick "rickman" Collins

snipped-for-privacy@XYarius.com
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Re: two questions
Rich, do you happen to live in SF bayarea? If so could you email me using
address of this posting?
I am looking for some help on FPGA.

Thanks,
Jimmy Zhang

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to
do up
pair
512



Re: two questions
Or, you can use the fast carry chain for the and.  The luts are (i0 xnor i1) and
(i2 xnor i3).  Lut outputs feed into the muxcy sel inputs, muxcy di<='0' and ci
comes from previous muxcy co.  First muxcy ci<='1', then your equality compare
comes out of the last muxcy.  Works out faster once you go over about 20 bit
inputs.

rickman wrote:

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--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
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