摘? 要: 介紹了數據收發器CY7B923/933的性能特點、結構原理、工作模式及應用電路。在一VME總線系統中,采用該收發器及UTP雙絞線實現了400Mbps的串行數據傳輸。
????關鍵詞: 點對點串行通信? 串行數據傳輸? 8B/10B編碼模式? 同步
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串行數據傳輸可實現長距離高速通信,且電纜線少、成本低、安裝方便,在計算機網絡中得到了廣泛應用,并日趨成為長距離數據通信的主要方式。CYPRESS公司的數據收發器CY7B923/933使用方便、可靠性好,可廣泛用于長距離高速點對點串行通信中,如光纖通信設備、工作站與海量存儲器的互連、視頻點播、語音圖像多媒體傳輸設備及其它長距離高速串行通信場合。CY7B923/933性能特點如下：
·適用于Fibre Channel、IBM ESCON、ATM;
·8B/10B編碼傳輸或不編碼直傳,傳輸速為160、330、400 Mbps三檔;
·最大傳輸距離(330Mbps的參考值)為:光纖幾千米,同軸電纜150米,屏蔽雙絞線80米,非屏蔽雙絞線40米;
·具有較強的自檢功能;
·單一+5V電源;
????·TTL同步I/O。
1 結構原理及功能
圖1是CY7B923的邏輯方塊圖,其功能是將8bit并行TTL輸入數據(D0～D7)轉換為PECL串行差分位流輸出。輸入寄存器用于輸入數據,時序與標準FIFO一致， 使能端
可選擇時鐘上升沿寫入數據。輸入數據由編碼器編碼為便于串行鏈路傳輸的8B/10B 傳輸碼,由SC/
(專用字/數據)端電平控制,將D0～D7輸入編成數據碼或專用字碼。時鐘發生器含有一個鎖相環PLL,將發送器時鐘CKW(數據按字節輸入的時鐘)十倍頻形成位時鐘,驅動移位寄存器。 移位寄存器將數據變成串行位流,分三路同時輸出,FOTO可關閉OUTA和OUTB輸出。自檢邏輯產生通信系統自檢用發送信號。
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圖2是CY7B933的邏輯方塊圖,其功能是將INA或INB 的PECL串行差分輸入位流轉換為8bit并行TTL數據輸出Q7～Q0。時鐘同步器內嵌鎖相環PLL跟蹤輸入數據位流的頻率,產生與發送時鐘同步的時鐘。移位寄存器按位接收串行數據,在同步時鐘作用下將數據按位送往成幀器" title="成幀器" target="_blank">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" 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title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器" title="成幀器">成幀器。成幀器使位流數據正確地按字節恢復。解碼器將成幀后的 8B/10B代碼解碼為原始數據或專用字,用RVS=H作數據違規或RD(Running Disparity)錯的報錯信號。串/并轉換后的數據從輸出寄存器Q7～Q0并行輸出。
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2 工作模式及8B/10B編碼
CY7B923/933有編碼、直傳兩種工作模式及自檢模式,由MODE、
端信號控制。
2.1 編碼模式
MODE=L,收發送器工作于8B/10B編碼模式,即8位數據或專用字由7B923編碼為10位的傳輸碼再逐位傳送。10位傳輸碼包括了所有256個8位組合,這些代碼符合ANSI X3.230(Fibre Channel)及IBM ESCON Channel規范。使用傳輸碼的優點是：(1)使傳輸過程1與0的數目均衡,每個8B的數據或專用字對應兩個10B的傳輸碼,用參數RD表征傳輸1及0的狀況。若1比0多則RD取正值,下一個字節發送0比1多的傳輸碼。反之,則RD取負值,下次發送1比0多的傳輸碼，這樣可保證傳輸的直流成分接近0,基線漂移減至最小;(2)附加位能保證串行位流中有足夠的躍變,使接收器能從這些躍變中恢復發送時鐘;(3)這種編碼大大增加了探測位錯或多位錯的可能性,一些專用字使用獨特的位組合,容易識別,可幫助接收器數據成幀;(4)可用同一種編碼傳輸數據或專用字。若為數據,SC/
端應加低電平,編碼使用數據字符集;若為專用字。編碼采用專用字代碼集,專用字符包含Fibre Channel、ESCON和其它專用系統以及用于診斷的所有協議字符。診斷字符可用于測試Fibre Channel等的連接、診斷系統對故障的響應、系統的時序等。8B數據或專用字編碼為10B傳輸碼通過查編碼表實現。對應于RD正負兩種取值,每個數據或專用字有兩種編碼,發送器先取正或負值為RD初值,根據要發送的數據或專用字及當前的RD值,查8B對應的10B代碼即實際發送的傳輸碼,并計算該傳輸碼的RD值作為當前值,與下一個要傳送的數據共同查表確定下一個傳輸碼。詳見參考文獻[1]。
2.2 直傳模式
MODE=H， 收發送器工作于直傳模式,即收發送器直接傳輸數據不編碼,編碼和解碼由外部協議控制器完成。輸入分成10位,數據需預先編碼,編碼方式任意,但需保證有足夠的躍變密度(每10位至少一次),使接收器鎖相環能正確鎖定相位,且編碼需與傳輸介質兼容。
無論是編碼模式還是直傳模式,若處于空閑狀態(時鐘CKW上升沿時
),編碼器將自動插入同步字K28.5(即C5.0)以保證接收器與發送器處在同步狀態。
2.3 自檢模式
,收發送器工作于自檢模式,7B923可分別發送兩種信號來檢測整個通信鏈路是否正常:一種是1與0相間的連續信號;另一種是循環發送的偽隨機序列信號。若為后者,7B923輸入寄存器轉換成線性反饋移位寄存器LFSR,它可產生一組511個字節的偽隨機代碼序列,包括了所有的數據字和專用字。7B933將輸出寄存器也變成LFSR,產生與發送器相同的偽隨機代碼序列,并與接收的序列相比較。若相同,則整個通信系統工作正常,否則為異常,使RVS=H給出錯誤信號。每次循環,7B923的
及7B933的
都將輸出一脈沖,此脈沖可用于記錄循環次數以控制自檢時間。7B923還可發送違規信號,以檢測報錯系統是否正常。這些信號都大大方便了故障診斷。
3 CY7B923/933應用電路
圖3為采用CY7B923/933實現的單向數據傳輸的應用電路。主機發送控制命令,通過控制邏輯控制CY7B923/933工作在傳輸或自檢模式。這里控制邏輯用FPGA實現,也可采用其它數字邏輯器件實現。控制電路應包含對、RVS端的檢測,以判斷系統工作正常與否,及時進行錯誤處理。主機數據傳輸速度一般與CY7B923/933不一致,發送端及接收端都需設置數據緩存,緩存一般用FIFO,我們采用CYPRESS公司的CY7C45X系列,它可與CY7B923/933組成無縫接口。若用FIFO的標志位作控制信號,則應注意標志延遲時間。CY7B933的輸出信號CKR,可作為其輸出數據寫入FIFO的時鐘,可作寫FIFO使能信號,使用的優點是同步字串到來它無效,自動濾除同步字串,這就保證了只將有效數據寫入FIFO， 避免同步字將FIFO填滿。電路板設計應采用四層板,CY7B923/933的位置應靠近雙絞線接口使連線最短,連線長度應盡量保持對稱。輸出輸入端都應接匹配電阻,如圖3所示。R1、R2阻值由下式給出:R1=(VccRt)/Vtt；R2=(VccRt)/(Vcc-Vtt)。式中,Rt為傳輸線阻抗；Vtt=Vcc-2V。如Vcc=5V,UTP雙絞線阻抗為110Ω,則R1=183Ω，R2=275Ω。
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發送數據前,先進行系統自檢,然后進入傳輸狀態。數據在發送時鐘CKW上升沿進入發送器,通過發送器的延遲為21tB-10ns(tB為移位時鐘周期，tB=1/10CKW),經傳輸線、變壓器進入接收器,數據通過接收器的延時為24tB+10ns。變壓器隔離傳輸線上可能的高電位,并有帶通濾波的作用。當7B933的RF=H,成幀器使能,成幀器開始搜尋數據流中的同步字K28.5,并以K28.5邊界為基準,確定后續數據的字節邊界。一些隨機錯誤可導致串行數據變成同步字K28.5,造成錯誤成幀。為避免出錯,可在數據同步過程中關閉成幀器,即令成幀器使能端RF=L,或令RF=H超過2048字節,此時需在連續5字節中有兩個K28.5才能啟動成幀功能,可大大減少偶然錯誤導致誤成幀。
作者在一VME總線長距離高速點對點串行通信系統中，采用最大數據傳輸率為330Mbps的標準CY7B923/933及UTP雙絞線,實現了400Mbps的串行數據傳輸,工作穩定可靠,誤碼率小于10-10。該工作是在中科院高能物理研究所過雅南研究員、趙棣新研究員的指導下完成的,在此表示衷心地感謝!
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參考文獻
1 HOTLink Transmitter/Receiver Data Sheet.Cypress Semiconductor? Corporation， 1997