There are seventy eight-bit numbers with exactly four 1's which means
that you can send 6 bits per byte. This may require a larger table
though (e.g. 64 entries for encode table and 256 entries for decode
table).

If you are sending only 4 bits per byte, you may have more evenly spaced
combinations such as Olin's 4 complement bits idea but interleaving the
data and the complement bits.

Tal

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Olin Lathrop
> Sent: Friday, September 12, 2003 4:17 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]:Manchester Lookup table
>
> ... Assuming the above is correct, you then decided to use
> manchester encoding on the 8 data bits because this is known
> to produce an equal number of 1s and 0s over short intervals.
>  This is the part that doesn't make sense. There are lots of
> ways to encode 4 bits into 8 so that there are always 4 0s
> and 4 1s.  I doubt the RF receiver will have a problem if the
> signal averages to 1/2 over an 8 bit interval instead of a 2
> bit interval.  Why not just send the 4 bits in the low nibble
> and the complement of the bits in the high nibble?  This
> makes both encoding and decoding trivial.  I have done
> exactly this with RF communication, and it worked fine.

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