Character codes, Encoder, Character codes –3 encoder –3 – Altera 8B10B Encoder/Decoder MegaCore Function User Manual
Page 21
Chapter 3: Specifications
3–3
Functional Description
May 2011
Altera Corporation
8B10B Encoder/Decoder MegaCore Function User Guide
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 3–3
). 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.
Table 3–1
lists the special K codes used by the MegaCore function.
Encoder
To encode an 8-bit word, the 8-bit value must be applied to the
datain
inputs and the
ena
input must be asserted (active high).
When one of the thirteen special 10-bit codes is to be inserted, the equivalent 8-bit
code is placed on the
datain
lines and the
kin
input is asserted. The MegaCore
function performs error checking to ensure the out-of-band 8-bit code is valid. If not,
the
kerr
output is asserted. See
Table 3–1
for a list of the valid K codes.
1
Although the 10B_ERR code is considered to be an invalid special character, it does
not cause the
kerr
signal to be asserted.
Idle (K28.5) characters can be automatically inserted when
ena
is not asserted by
asserting the
idle_ins
input.
Table 3–1. Character Codes
10-Bit Special K Codes
Equivalent 8-Bit Codes
K28.0
8'b000_11100
K28.1 8'b001_11100
K28.2 8'b010_11100
K28.3
8'b011_11100
K28.4
8'b100_11100
K28.5
(1)
8'b101_11100
K28.6
8'b110_11100
K28.7
8'b111_11100
K23.7
8'b111_10111
K27.7
8'b111_11011
K29.7
8'b111_11101
K30.7
8'b111_11110
10B_ERR
8'b111_11111
Note to
Table 3–1
:
(1) K28.5 is a comma character used for alignment purposes, and to represent the IDLE code.