A：HDMI傳輸原理
1.HDMI採用TMDS (Time Minimized Differential Signal)最小化傳輸差分信號傳輸技術 , TMDS是一種微分信
號機制,採用的是差分傳動方式 ,是一種利用2個引腳間電壓差來傳送信號的技術。
2.每一個標準的HDMI連接,都包含了3個用於傳輸數據。的TMDS傳輸通道,還有1個獨立的TMDS時鐘通道,
以保證傳輸時所需的統一時序。在一個時鐘週期內,每個TMDS通道都能傳送10bit的數據流。而這10bit數據,可以由若干種不同的編碼格式構成。
As shown in Figure 5-1, an HDMI link includes three TMDS Data channels and a single TMDS Clock channel. The TMDS Clock channel constantly runs at a rate proportional to the pixel rate of the transmitted video. During every cycle of the TMDS Clock channel, each of the three TMDS data channels transmits a 10-bit character. This 10-bit word is encoded using one of several different coding techniques.
The input stream to the Source’s encoding logic will contain video pixel, packet and control data.
The packet data consists of audio and auxiliary data and associated error correction codes.
These data items are processed in a variety of ways and are presented to the TMDS encoder as either 2 bits of control data, 4 bits of packet data or 8 bits of video data per TMDS channel. The Source encodes one of these data types or encodes a Guard
Band character on any given clock cycle.
一般來說,HDMI 傳輸的編碼格式中要包含視頻數據(HDMI1.3 版本前每個像素採用
24bit)、控制數據和數據包(數據包中包含音頻數據和附加信息數據,例如糾錯碼等)。
TMDS 每個通道在傳輸時要包含一個 2bit 的控制數據、8bit 的視頻數據或者 4bit 的數據包即可。在 HDMI 信息傳輸過程中,可以分爲三個階段:視頻數據傳輸週期、控制傳輸週期和數據島傳輸週期,分別對應上述的三種數據類型。
