HDMI Detailed introduction-Transmission Period

Wed Dec 07 16:33:22 CST 2022

HDMI Detailed introduction-Transmission Period

HDMI Transmission Period

TMDS data transmission for HDMI can be divided into three transmission periods.

1_HDMI-3-TMDS-Periods-HornmicLink

Different HDMI data is sent in the TMDS data channel in three different periods: Video Data Period, Data Island Period, and Control Period.

1. Video Data Period: Transfer of active Video Data.

2. Data Island Period: Audio and auxiliary data are transmitted through a series of Data Islands, which will also have Hsync and Vsync.

3. Control Period: The control period is used when there is no video, audio or auxiliary data to be transmitted. Hsync, Vsync are transmitted during this period, and Preamble is transmitted at the end of the period.

Note: A Control Period is required between any two cycles of the non-control period.

The overall TMDS Period of video Frame is as follows.

2_Overall-TMDS-Periods-in-Video-Frame

The Blanking is the display trailing edge and display leading edge and synchronization in VGA timing.

3_HDMI-Synchronization-Timing

The transactions for the three transmission periods are as follows.

4_Transactions-of-the-three-TMDS-Periods

  • 1. The left is Control Period, transfer data: Hsync, Vsync & Preamble.

  • 2. The middle is the Data Island period, the transmission has Hsync, Vsync, and two Packet Header and Packet (every 32 clocks per packet); in addition, the two ends of the Data Island will be protected with Guard Band and separated from the Data Island data, because most of the data transmitted at this stage is very important, such as the image resolution, which determines the display of the Video Data data later.

  • 3. On the right is Video Data Island, which transmits video pixel data and also has Guard Band at the beginning of the period.

Data Island Packet Structure

The structure of the Data Island Packet is shown in the following figure.

5_Data-Island-Packet-structure

All Data Island Packets are transmitted in one period of 32 clock pulses, which means that one packet is transmitted in every 32 clocks.

Take the above figure as an example.

1. Packet header is BCH block 4, transmitted by Channel 0[2], 32clk means there are 32bits, which it is 4 bytes, the first three bytes is packet header, the last byte is Check Digit.

2. The packet body is BCH block 0,1,2,3, which is transmitted by Channel 1 and Channel 2 with 8 lines respectively, with a total of 24 bytes and 6 bytes of Check Digits.

3. Parity Bits check code is used to check whether the HDMI Cable transmission process with errors, if the Packet in the HDMI receiver detect error, if only one bit of error, then can be corrected, more than 1 bit of error will be identified as an invalid Packet.

Therefore, the receiver needs to take out the Parity bit of each BCH block after the packet is unpacked and perform Calibration.



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By HornmicLink_Henry @221207 16:42