A：HDMI传输原理
1.HDMI采用TMDS (Time Minimized Differential Signal)最小化传输差分信号传输技术 , TMDS是一种微分信
号机制,采用的是差分传动方式 ,是一种利用2个引脚间电压差来传送信号的技术。
2.每一个标准的HDMI连接,都包含了3个用于传输数据。的TMDS传输通道,还有1个独立的TMDS时钟通道,
以保证传输时所需的统一时序。在一个时钟周期内,每个TMDS通道都能传送10bit的数据流。而这10bit数据,可以由若干种不同的编码格式构成。
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.
一般来说,HDMI 传输的编码格式中要包含视频数据(HDMI1.3 版本前每个像素采用
24bit)、控制数据和数据包(数据包中包含音频数据和附加信息数据,例如纠错码等)。
TMDS 每个通道在传输时要包含一个 2bit 的控制数据、8bit 的视频数据或者 4bit 的数据包即可。在 HDMI 信息传输过程中,可以分为三个阶段:视频数据传输周期、控制传输周期和数据岛传输周期,分别对应上述的三种数据类型。
