PRELIMINARY
CYP15G0401RB
Document #: 38-02111 Rev. ** Page 27 of 35
X3.230 Codes and Notation Conventions
Information to be transmitted over a serial link is encoded eight
bits at a time into a 10-bit Transmission Character and then
sent serially, bit by bit. Information received over a serial link
is collected ten bits at a time, and those Transmission
Characters that are used for data characters are decoded into
the correct eight-bit codes. The 10-bit Transmission Code
supports all 256 eight-bit combinations. Some of the remaining
Transmission Characters (Special Characters) are used for
functions other than data transmission.
The primary use of a Transmission Code is to improve the
transmission characteristics of a serial link. The encoding
defined by the Transmission Code ensures that sufficient
transitions are present in the serial bit stream to make clock
recovery possible at the Receiver. Such encoding also greatly
increases the likelihood of detecting any single or multiple bit
errors that may occur during transmission and reception of
information. In addition, some Special Characters of the Trans-
mission Code selected by Fibre Channel Standard contain a
distinct and easily recognizable bit pattern that assists the
receiver in achieving character alignment on the incoming bit
stream.
Notation Conventions
The documentation for the 8B/10B Transmission Code uses
letter notation for the bits in an eight-bit byte. Fibre Channel
Standard notation uses a bit notation of A, B, C, D, E, F, G, H
for the eight-bit byte for the raw eight-bit data, and the letters
a, b, c, d, e, i, f, g, h, j for encoded 10-bit data. There is a
correspondence between bit A and bit a, B and b, C and c, D
and d, E and e, F and f, G and g, and H and h. Bits i and j are
derived, respectively, from (A,B,C,D,E) and (F,G,H).
The bit labeled A in the description of the 8B/10B Transmission
Code corresponds to bit 0 in the numbering scheme of the
FC-2 specification, B corresponds to bit 1, as shown below.
FC-2 bit designation— 7 6 5 4 3 2 1 0
HOTLink D/Q designation—7 6 5 4 3 2 1 0
8B/10B bit designation— H G F E D C B A
To clarify this correspondence, the following example shows
the conversion from an FC-2 Valid Data Byte to a Transmission
Character.
FC-2 45H
Bits: 7654
3210
0100 0101
Converted to 8B/10B notation, note that the order of bits has
been reversed):
Data Byte Name D5.2
Bits: ABCDE
FGH
10100 010
Translated to a transmission Character in the 8B/10B Trans-
mission Code:
Bits: abcdei fghj
101001 0101
Each valid Transmission Character of the 8B/10B Trans-
mission Code has been given a name using the following
convention: cxx.y, where c is used to show whether the Trans-
mission Character is a Data Character (c is set to D, and SC/D
= LOW) or a Special Character (c is set to K, and SC/D = HIGH).
When c is set to D, xx is the decimal value of the binary number
composed of the bits E, D, C, B, and A in that order, and the y
is the decimal value of the binary number composed of the bits
H, G, and F in that order. When c is set to K, xx and y are
derived by comparing the encoded bit patterns of the Special
Character to those patterns derived from encoded Valid Data
bytes and selecting the names of the patterns most similar to
the encoded bit patterns of the Special Character.
Under the above conventions, the Transmission Character
used for the examples above, is referred to by the name D5.2.
The Special Character K29.7 is so named because the first six
bits (abcdei) of this character make up a bit pattern similar to
that resulting from the encoding of the unencoded 11101
pattern (29), and because the second four bits (fghj) make up
a bit pattern similar to that resulting from the encoding of the
unencoded 111 pattern (7). This definition of the 10-bit Trans-
mission Code is based on the following references.
A.X. Widmer and P.A. Franaszek. “A DC-Balanced, Parti-
tioned-Block, 8B/10B Transmission Code” IBM Journal of
Research and Development, 27, No. 5: 440-451 (September,
1983).
U.S. Patent 4,486,739. Peter A. Franaszek and Albert X.
Widmer. “Byte-Oriented DC Balanced (0.4) 8B/10B Parti-
tioned Block Transmission Code” (December 4, 1984).
Fibre Channel Physical and Signaling Interface (ANS
X3.230-1994 ANSI FC-PH Standard).
IBM Enterprise Systems Architecture/390 ESCON I/O
Interface (document number SA22-7202).
8B/10B Transmission Code
The following information describes how the tables are used
for both generating valid Transmission Characters (encoding)
and checking the validity of received Transmission Characters
(decoding). It also specifies the ordering rules to be followed
when transmitting the bits within a character and the
characters within any higher-level constructs specified by a
standard.
Transmission Order
Within the definition of the 8B/10B Transmission Code, the bit
positions of the Transmission Characters are labeled a, b, c,
d, e, i, f, g, h, j. Bit “a” is transmitted first followed by bits b, c,
d, e, i, f, g, h, and j in that order.
Note that bit i is transmitted between bit e and bit f, rather than
in alphabetical order.
Valid and Invalid Transmission Characters
The following tables define the valid Data Characters and valid
Special Characters (K characters), respectively. The tables
are used for both generating valid Transmission Characters
and checking the validity of received Transmission
Characters. In the tables, each Valid-Data-byte or
Special-Character-code entry has two columns that represent
two Transmission Characters. The two columns correspond to
the current value of the running disparity. Running disparity is
a binary parameter with either a negative (–) or positive (+)
value.
After powering on, the Transmitter may assume either a
positive or negative value for its initial running disparity. Upon
transmission of any Transmission Character, the transmitter
will select the proper version of the Transmission Character
based on the current running disparity value, and the Trans-
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