Advanced understanding of HDMI

HDMI chips are divided into transmitter and receiver if they are separated independently. The typical ep901 is an HDMI receiver integrated with the HDCP engine and digital audio decoder. Its HDCP is read and verified by the HDMI user, and it is on the slave side.

The above is an internal chart of ep901, which is integrated with the HDCP engine to communicate with the HDMI sender. When the chip is powered on or reset, its internal RAM first reads the HDCP key and bksv from the external 24c08. Then, handshaking is performed with the HDMI source through the IIC interface of DDC, and communication starts after the communication is successful.
For the sake of confidentiality, the contents in 24c08 are pre-encrypted and burned to ee, and all the Manual reads are 0xff. This file is generally provided by the vendor. Because it only serves as the key, you only need to install the same HDCP in batch production (different from the unique verification code mechanism ), the editing of the HDCP itself requires the authorization of the upper-level organization.
HDMI only provides a data transmission mechanism. As for the transmitted data, both parties agree that both ybppr and RGB can be transmitted, both of which are analog signals transmitted by digital means, such as grayscale signals, and y can be used to measure waveforms, in addition, high-definition synchronization is required. Generally, a low synchronization (using a low-pass filter) is separated from the y channel at the same time. In addition, HDCP solves the problem of abnormal image display (black screen after playing), while edid of HDMI solves the problem of abnormal sound.
When debugging ep901, a symptom was found. The DVI signal was input to ep901. When the input is RGB, the display is normal. When the input is ypbpr, the color is abnormal. This is because the DVI signal only has VGA, svga, XGA, sxga, and other RGB signals, and does not include the ypbpr signal (which is included in HDMI). Of course, the processing is abnormal. When the 8-59B signal generator is used to set the output, the default VGA also has the output when the DVI is set. If it is set to RGB, only the VGA has the output.