Xilinx V2.1 User Manual
Page 67
Communication
67
Xilinx Blocks
♦
IESS-308 (225): implements IESS-308 specification (225, 205) shortened RS
code.
•
Symbol Width
: specifies the symbol width for the RS code. The RS encoder
supports symbol width from 3 to 12.
•
n
: specifies the length of the RS code. The RS encoder supports code with length
from (2
sw
- 1) to 3, where sw is symbol width.
•
k
: specifies the number of information symbols in a RS code. The RS encoder
supports code with length from (n-2) to max((n-256), 1).
•
Field Polynomial
: specifies the field polynomial used to generate the Galois
field for the code. It is entered as an binary array where the 1st element
corresponds to the highest degree of the polynomial. A value of zero causes the
default polynomial for the given symbol width to be selected. The specified
polynomial should be a primitive polynomial for the given symbol width. The
default polynomials for the specified symbol width are:
•
Generator Start
: specifies the Galois field logarithm of the first root of the
generator polynomial g(x), i.e.:
where
a = a primitive root of the Galois field for the code
GS
= Generator Start
h
= Scaling Factor. Normally, Generator_Start is 0 or 1; however, it can be any non-
negative integer between 0 and (2
16
- 1).
•
Scaling Factor
: Scaling factor for the generator polynomial root index.
Normally h is 1; however, it can be any positive integer between 1 and (2
16
- 1).
•
Provide Reset Pin
: when checked, the block has optional start and bypass
input pins.
Symbol Width
Default Polynomials
Array Representation
3
x
3
+ x + 1
[1 0 1 1]
4
x
4
+ x + 1
[1 0 0 1 1]
5
x
5
+ x
2
+ 1
[1 0 0 0 1 1]
6
x
6
+ x + 1
[1 0 0 0 0 1 1]
7
x
7
+ x
3
+ 1
[1 0 0 0 1 0 0 1]
8
x
8
+ x
4
+ x
3
+ x
2
+ 1
[1 0 0 0 1 1 1 0 1]
9
x
9
+ x
4
+ 1
[1 0 0 0 0 1 0 0 0 1]
10
x
10
+ x
3
+ 1
[1 0 0 0 0 0 0 1 0 0 1]
11
x
11
+ x
2
+ 1
[1 0 0 0 0 0 0 0 0 1 0 1]
12
x
12
+ x
6
+ x
4
+ x + 1
[1 0 0 0 0 0 1 0 1 0 0 1 1]
g x
( )
x
a
hx GS
i
+
(
)
–
(
)
i
0
=
n
k
–
1
–
∏
=