Cypress CYV15G0404DXB manual X3.230 Codes and Notation Conventions, 8B/10B Transmission Code

CYV15G0404DXB

X3.230 Codes and Notation Conventions

Information 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 8-bit codes. The 10-bit transmission code supports all 256 8-bit combinations. Some of the remaining transmission characters (special characters) are used for functions other than data trans- mission.

The primary use of a transmission code is to improve the trans- mission 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 transmission 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 8-bit byte. Fibre Channel Standard notation uses a bit notation of A, B, C, D, E, F, G, H for the 8-bit byte for the raw 8-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—76543210 HOTLink D/Q designation—76543210 8B/10B bit designation—HGFEDCBA

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 Transmission Code has been given a name using the following convention: cxx.y, where c is used to show whether the Transmission 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.

Using these 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).

Note. This definition of the 10-bit transmission code is based on the following references, which describe the same 10-bit trans- mission code.

■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 Partitioned 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 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 trans-

Document #: 38-02097 Rev. *B Page 36 of 44

[+] Feedback