Jon Baker <PICLIST@mitvma.mit.edu> wrote:

> Same ( or silimar) encoding is used on CDs which I've done a lot of
> reading about.

    Not exactly; CDs use Reed-Solomon encoding, not simple Hamming
    codes.  Same basic idea, though; redundancy is added in order to
    correct errors.

> What I _would_ like to know is: is there a standard for where the
> hamming bits and data bits are placed relative to each other.. are they
> interleaved etc..
>
> In your example all the hamming bits come first but is this the case
> for say an 18/24 code?

    Positioning of the bits within a codeword is unimportant.  You
may
    want to interleave the bits from multiple codewords -- that'll
help
    with burst errors, since a burst of n errors will only affect one
bit
    from each of n words -- but if you're asking whether the data and
    check bits should be interleaved within each codeword, the
answer's
    probably no.  Arranging them as I did has HUGE benefits if you're
    doing your decoding in software and are concerned with decode
speed.

    -Andy

    P.S.  If you're using 18,24 Hamming, you won't be able to get
          anywhere near 7Mb/s encoding or decoding with a PIC.

=== Andrew Warren -- aiw@cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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