ORT82G5-1BM680C LATTICE [Lattice Semiconductor], ORT82G5-1BM680C Datasheet - Page 15

• Manufacturer Part Number: ORT82G5-1BM680C
• Description: 0.6 to 3.7 Gbps XAUI and FC FPSCs
• Manufacturer: LATTICE [Lattice Semiconductor]

Lattice Semiconductor
Following the definitions and conventions used in defining the 8b/10b coding rules, each valid coded character has
a name corresponding to its 8-bit binary value:
• Dxx.y for data characters
• Kxx.y for special characters
• xx = the 5-bit input value, base 10, for bits ABCDE
• y = the 3-bit input value, base 10, for bits FGH
An 8b/10b encoder is designed to maintain a neutral average disparity. Disparity is the difference between the
number of 1s and 0s in the encoded word. Neutral disparity indicates the number of 1s and 0s are equal. Positive
disparity indicates more 1s than 0s. Negative disparity indicates more 0s than 1s. The average disparity deter-
mines the DC component of the signals on the serial line. Running disparity is a record of the cumulative disparity
of every encoded word, and is tracked by the encoder.
In order to maintain neutral disparity, two different codings are defined for each data value. The 8b/10b encoder in
the transmit path selects between (+) and (-) encoded word based on calculated disparity of the present data to
maintain neutral disparity
In the receive path, the clock and data recovery blocks retime the incoming data and 8b/10b decoders generate 8-
bit data based on the received 10-bit data. A sequence of valid 8b/10b coded characters has a maximum run
length of 5 bits (i.e., 5 consecutive ones or 5 consecutive zeros before a mandatory bit transition). This assures
adequate transitions for robust clock recovery.
The recovered data is aligned on a 10-bit boundaries by detecting and aligning to special characters in the incom-
ing data stream. Data is word aligned using the comma (/K/) character. A comma character is a special character
that contains a unique pattern (0011111 or its complement 1100000) in the 10-bit space that makes it useful for
delimiting word boundaries. The special characters K28.1, K28.5 and K28.7 contain this comma sequence and are
treated as valid comma characters by the SERDES.
The following table shows all of the valid special characters. All of the special characters are made available to the
FPGA logic; however only the comma characters are used by the SERDES logic. The different codings that are
possible for each data value are shown as encoded word (+) and encoded word (-). The table also illustrates the
8b/10b bit labeling convention. The bit positions of the 8-bit characters are labeled as H,G,F,E,D,C,B and A and the
bit positions of the 10-bit encoded characters are labeled as a, b, c, d, e, i, f, g, h, and j. The encoded words are
transmitted serially with bit ‘a’ transmitted first and bit ‘j’ transmitted last.
Table 2. Valid Special Characters
K28.0
K28.1 /comma/
K28.2
K28.3 /A/
K28.4
K28.5 /comma/
K28.6
K28.7 /comma/
K23.7
K27.7
K29.7
K30.7
K Character
HGF EDCBA
765 43210
000 11100
001 11100
010 11100
011 11100
100 11100
101 11100
110 11100
111 11100
111 10111
111 11011
111 11101
111 11110
K Control
15
1
1
1
1
1
1
1
1
1
1
1
1
ORCA ORT42G5 and ORT82G5 Data Sheet
Encoded Word (–)
001111 0100
001111 1001
001111 0101
001111 0011
001111 0010
001111 1010
001111 0110
001111 1000
111010 1000
110110 1000
101110 1000
011110 1000
abcdei fghj
Encoded Word (+)
110000 1011
110000 0110
110000 1010
110000 1100
110000 1101
110000 0101
110000 1001
110000 0111
000101 0111
001001 0111
010001 0111
100001 0111
abcdei fghj