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本文始於2013年，討論Typical PRBS (Pseudo Random Binary Sequence)與RGB PRBS的差異，並且在Designer v8分別該如何使用它。This article is intended to introduce how to use PRBS and RGB PRBS in Designer v8.

1. RGB PRBS

2. Typical PRBS

3. Conclusions

4. 問題與討論

   4.1 What does the "do_encoding" setting work for?

   4.2 How to use "TAPS" setting of V_PRBS_JITTER in Designer?

   4.3 為何EYESOURCE元件與V_PRBS/V_PRBS_JITTER產生pattern的方式不同?

   4.4 How to use PRBS with defined "PRBS length" in Designer V_PRBS/V_PRBS_JITTER?

5. 參考資料

1. RGB PRBS 

RGB PRBS is used by default for the old components as V_PRBS and V_PRBS_JITTER.

No matter "Bitlist" or "Bitfile" is present or not, random pattern can be generated and it is affected by "SEED".

If you want to use a typical PRBS pattern (as PRBS7), just to include it by "Bitfile".

On the other hand, you can also set TAPs to generate PRBS7 pattern, please refer 4.2.

2. Typical PRBS 

Typical PRBS cab be used easily for the new components as EYESOURCE and AMISOURCE.

3. Conclusions 

• "RGB PRBS" and "Typical PRBS" are different, but Designer can support both of them.
• "RGB PRBS" and "Typical PRBS" are both affected by "SEED" (default 0), but just "Typical PRBS" is defined by "PRBS length"(2~31).
• When  BITLIST or BITFILE are used, any SEED value will be ignored.
• The PRBS_BITLENGTH parameter specifies the total number of bits to be generated. The default is (2^PRBS_NO -1). For example, PRBS7 means it's PRBS_BITLENGTH=2^7-1 random bit stream.
• If both the BITFILE and the BITLIST parameters are set, the BITFILE will be used.

Designers的GUI與Help內的用字並沒有統一，容易混淆；實際上"PRBS_BITLENGTH"="Number of bits to generate", "PRBS_NO"="PRBS length"

4. 問題與討論

4.1 What does the "do_encoding" work for?

Ans：8b/10b encoding is another coding method, if you use this setting, the original bit pattern will be coded by 8b/10b encoding.

4.2 How to use "TAPs" setting of V_PRBS_JITTER in Designer?

Ans： First, set "SEED">0. Second, set TAPs=[7, 6] for PRES7=X⁷+X⁶+1

4.3 為何EYESOURCE元件與V_PRBS/V_PRBS_JITTER產生pattern的方式不同?

Ans：EYESOURCE是較新開發的元件，功能比較齊全，以後就少用V_PRBS與V_PRBS_JITTER了。 另外，直接import IBIS model的symbol內的屬性設定，一樣可以設input PRBS pattern

4.4 How to use PRBS with defined "PRBS length" in Designer V_PRBS/V_PRBS_JITTER

Ans：Use Matlab to generator PRBS pattern and include it by "bitfile" of V_PRBS, or set LFSR by TAPs.

5. 參考資料 

• PRBS生成原理介紹

• 偽亂數二進為序列

• High Speed Serdes Devices and Applications

PRBS7=X⁷+X⁶+1

PRBS11=X¹¹+X⁹+1

PRBS15=X¹⁵+X¹⁴+1