Maxim-integrated HFAN-09.5.0: Pattern Creator/Converter Software Instrukcja Użytkownika Pobierz pdf (Strona 3)

Application Note HFAN-9.5.0 (Rev.1; 04/08) Maxim Integrated

Page

3 of 8

2.1 PRBS Patterns

The Pseudo Random Bit Sequences (PRBS) are

generated using a software version of the

conventional hardware shift register with the taps of

minimum shift algorithms generated from Galois-

field arithmetic (Figure 2, Table 1, see References 1

& 2). The shift register length is determined by the

pattern title. For example, a PRBS 2

-1 pattern

would be generated using a shift register 7 bits long.

Where n is the register length, the PRBS pattern

contains every possible combination of n bits

(except one).

n n-1 2 13

XOR

SHIFT DIRECTION

TAP1

TAP2

TAP3

TAP4

OUT

n Bit Shift Register

PRBS Generation

Figure 2. PRBS Generation

The mark density (100%*(number of ones / total

bits)) and the transition density (100%*(number of

bit transitions / total number of bits)) of PRBS

patterns are approximately 50%. This approximation

improves as the pattern length (shift register length)

increases. Also, the maximum number of

consecutive identical digits (CIDs) is equal to the

-1 PRBS has a

maximum of 23 CIDs).

Pressing any of the PRBS buttons opens the option

list shown in Figure 3. Using this option list, the

PRBS sequence can be repeated an integer number

of times or the total number of bits to write of the

given PRBS can be selected. The PRBS can also be

written to the file inverted or non-inverted. It is

important to note that the mark density and the

transition density of the pattern sequence can deviate

from the 50% approximations if only part of the

PRBS is written to the file.

Table 1: PRBS Pattern Length / Tap Positions

Len

gth

(n)

Pattern

Length

-1) Tap1 Tap2 Tap3 Tap4

3 7 3 2

4 15 4 3

5 31 5 3

6 63 6 5

7 127 7 6

8 255 8 7 3 2

9 511 9 5

10 1023 10 7

11 2047 11 9

12 4095 12 9 8 5

13 8191 13 12 10 9

14 16383 14 13 3 2

15 32767 15 14

16 65535 16 14 13 11

17 131071 17 14

18 262143 18 11

19 524287 19 18 14 13

20 1048575 20 17

21 2097151 21 19

22 4194303 22 21

23 8388607 23 18

Fig

ure 3. PRBS Options

In this software program, each PRBS register is

initialized with all 1’s. Therefore, each PRBS

sequence will start with the maximum CID length

(e.g. the first seven bits generated from the non-

inverted PRBS 2^7-1 will be all ones).

1 2 3 4 5 6 7 8

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