Crestron DM-RX1-1G Specifications download pdf (Page 8)

Crestron DigitalMedia™ Design Guide

4 Check website (www.crestron.com) for product availability

The complexity of HDMI becomes obvious when you compare HDMI cable to analog audio and video cables. Analog cables

typically consist of one to three wire pairs, depending on the format, and they simply carry an audio or video signal (not both).

In contrast, the HDMI cable consists of 19 wires, which carry high speed video, audio and other digital information. The digital

audio and video data is encoded into three color channels and a clock channel. Audio is embedded inside the video data and is

inserted and extracted at each end. Additional information carried by HDMI includes:

DDC: The Data Display Channel (DDC) is a two-way communications interface between the source and the downstream

repeater or display device. This channel was originally provided to communicate device capability information, which is

encoded in a structure known as Extended Display Identification Data (EDID). HDMI devices use EDID to indicate what audio

and video formats they support, discussed in more detail in a later section. The DDC interface is also used to set up and

maintain HDCP encryption.

Hot Plug Detect: The downstream device, or sink, indicates its presence to the source with the Hot Plug Detect (HPD)

signal. This allows each device to know when a cable has been connected and to start authentication.

CEC: Consumer Electronics Control (CEC) channel wiring is mandatory, although implementation of CEC in a product is

optional. The CEC channel uses the industry standard AV Link protocol for remote control functions, and is a one wire

bidirectional serial bus. The CEC feature allows the user to command and control multiple CEC-enabled boxes with one

remote control, and individual CEC-enabled boxes to command and control each other without user intervention.

Depending on the device and manufacturer, DDC, HPD, and CEC signals interact differently. This inconsistency can

negatively affect device performance.

Additional control signals are associated with HDMI, but they are beyond the scope of this guide.

Topology

Every HDMI installation consists of at least one content source, like a cable box or Blu-ray player, and a sink, like a TV or a

projector. Most custom installations also involve at least one repeater, which is a device that accepts and re-transmits HDMI

content. Repeaters include simple devices such as switches and distribution amplifiers as well as more feature-rich devices

like audio and video processors.

EDID

EDID is the information transmitted from a display to a source conveying its resolution capabilities. Initially developed for

computers and monitors, EDID has made its way into consumer electronic devices via HDMI. HDMI displays and surround

sound receivers use EDID to communicate their audio and video capabilities. For instance, a television may use EDID

to indicate support for the standard HD resolutions plus 1080p and Deep Color. Another TV may not accept higher than

720p/1080i resolution. One audio processor may support Dolby TrueHD while another only supports standard Dolby;

most TVs only support basic stereo audio. All of this information is stored in EDID.

The content source reads and analyzes EDID to determine what formats to send. It is the responsibility of the source, if

equipped, to only send formats that the downstream devices support. For example, Blu-ray players include video scalers to

best match the disc’s native format to the capabilities of the television or projector.

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Crestron DM-RX1-1G Specifications Page 8