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Basic Design of HDMI
HDMI Initialization Sequence
HDMI Design and Initialization Sequence is the second document in a series of HDMI whitepapers published by
CEDIA. The first document, Introduction to HDMI Interface, introduced HDMI standards and labeling guidelines.
The objective of this document is to discuss the basic design of HDMI devices, the HDMI initialization sequence,
and features in the HDMI 1.4a specification. A HDCP key limits guide is located in Appendix C.
HDMI-compliant devices can be categorized into 3 types: sources, sinks and repeaters. Each device has one or
more receiver(s) and/or transmitter(s), or it may contain both a receiver and a transmitter.
The source sends the content to be displayed. Examples of sources include set-top boxes, media servers, Blu-ray
disc players, and computer graphic cards. A source only has an HDMI transmitter.
The sink receives the content from the source and provides it to the display so it can be viewed. Examples of a
sink device include TVs and digital projectors. A sink can have one or more HDCP/HDMI receivers.
A repeater accepts content, decrypts it, then re-encrypts and finally retransmits the data [1]. A repeater may also
perform some signal processing, such as up-converting video into a higher-resolution format, or splitting out the
audio portion of the signal [1]. Repeaters have both HDMI inputs and outputs. Examples include A/V receivers that
separate and amplify the audio signal while also retransmitting the video for display on a TV. A repeater can also
transmit the protected content to multiple outputs for simultaneous display on several screens [1].
During the authentication process, a source device and a sink device exchange their unique set of keys to deter-
mine the highest resolution (best possible format), correct audio outputs, and HDCP compliance. This process is
depicted in figure 1 (see Appendix B for larger version).
The connection process begins when the source outputs a +5V signal on pin 18 to the sink, which sends back
the +5V signal to the source on pin 19, which is the hot plug detect pin. If the hot plug is asserted, the source will
read the capabilities of the sink device (see Figure 2). The capabilities are listed in the sink’s EDID, which contains
a multitude of information, including the acceptable video format(s), audio formats, and lip-sync delays. To learn
more about EDID, see CEDIA’s Introduction to HDMI whitepaper.
After the EDID is read properly, the source will send about 30 frames of unencrypted video to initialize the HDCP
register of the sink device [5]. The source then typically reads the sink’s HDCP BCAPS register to determine if the
downstream device it is connected to is a display device or a repeater device [5]. Reading the BCAPS register is
important because the repeater bit value is used in the calculation of the Ro value [5]. Ro is a register value used to
compare the source and sink and determine whether the HDCP authentication has been completed successfully.
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