One of the goodies! For those who don't have ready access to a patent
database:
There's one available to all right here:
http://www.uspto.gov/patft/index.html and it's still free.
Title: Byte oriented DC balanced (0,4) 8B/10B partitioned
block transmission code
Published: 1984-12-04
Filed: 1982-06-30
Inventor: Franaszek, Peter A.; Katonah, NY
Widmer, Albert X.; Katonah, NY
Abstract: A binary DC balanced code and an encoder circuit for
effecting same is described, which translates an 8 bit
byte of information into 10 binary digits for transmission over
electromagnetic or optical transmission lines subject to timing
and low frequency constraints. The significance of this code is
that it combines a low circuit count for implementation with
excellent performance near the theoretical limits, when measured
with the commonly accepted criteria. The 8B/10B coder is
partitioned into a 5B/6B plus a 3B/4B coder. The input code
points are assigned to the output code points so the number of
bit changes required for translation is minimized and can be
grouped into a few classes.
And from the start of the Background section:
"The primary purpose of transmission codes is to transform the frequency
spectrum of a serial data stream so that clocking can be recovered readily
and AC coupling is possible. The code must also provide special characters
outside the data alphabet for functions such as character synchronization,
frame delimiters and perhaps for abort, reset, idle, diagnostics, etc.
Codes are also used, often in combination with signal waveform shaping, to
adapt the signal spectrum more closely to specific channel requirements. In
most cases a reduction in bandwidth by constraints on both the high and the
low frequency components is desirable to reduce distortion in the
transmission media, especially electromagnetic cables, or in the band
limited receiver, and to reduce the effects of extrinsic and intrinsic
noise.
Another aspect of codes is their interaction with noise and errors in the
line digits. The redundancy associated with line codes can be used to
supplement other error detection mechanisms or to monitor the quality of
the channel with a minimal amount of circuitry.
Such codes generally exhibit the undesirable feature of enlarging error
bursts in the decoded data, making detection by a cyclic redundancy check
more difficult. A good transmission code should minimize these effects."
Now we are all wiser... thanks to Kai and Keith.;-)
. I use Delphion (which