Specifications
Figure 3–2. 8B10B Encoder/Decoder GFP Typical Application
Ingress
Egress
Transport Network
GFP Data Stream
(64B/65B Encoded)
Gigabit
Ethernet
Stream
Gigabit
Ethernet
Stream
GFP
Demapper
8B/10B
Encoder
8B/10B
GFP
Decoder
Mapper
(8B/10B Encoded)
(8B/10B Encoded)
On ingress to the transport network, if the decoder receives an
unrecognized codeword, such as an illegal codeword or a legal codeword
with a running disparity error, it asserts the kerror rderrsignals
respectively. By asserting these error signals, the decoder indicates to the
mapper that an invalid codeword has been received, the mapper then
generates a special control character, the 10B_ERR code. In addition, the
mapper remaps the 8B/10B codewords into 64B/65B codewords before
sending the data to the transport network.
On egress from the transport network, the demapper decodes the
64B/65B codewords and sends them to the 8B/10B encoder. When the
encoder receives the 10B_ERR code, it sends out one of the two 10-bit
illegal codewords with neutral disparity: 001111 0001(RD-) or 110000
1110(RD+), depending on the running disparity.
Character Codes
In addition to 256 data characters, the 8b/10b code defines thirteen out-
of-band indicators, also called special control characters. The 256 data
characters are named Dx.y, and the special control characters are named
Kx.y—except for the special code 10B_ERR (see Table 3–1 on page 3–4).
The x value corresponds to the five-bit group, and the y value to the three-
bit group.
The special control characters indicate, for example, whether the data is
idle, test data, or data delimiters. In applications where encoded
characters are transmitted bit-serially, the comma character (K28.5) is
usually used for alignment purposes as its 10-bit code is guaranteed not
to occur elsewhere in the encoded bit stream, except after K28.7 which is
normally only sent during diagnostic.
Altera Corporation
October 2007
MegaCore Version 7.2
3–3
8B10B Encoder/Decoder MegaCore Function User Guide
ALTERA [ ALTERA CORPORATION ]
