How Different is HDMI 1.4 from 1.3?
Jeff Boccaccio says "very little has actually changed" between the two specs.
Very little has actually changed. In the case of HDMI Rev. 1.4 with Ethernet, a couple of interesting capabilities have been added. In the case of Rev. 1.4 without Ethernet, however, there is no difference. The new Rev 1.4 spec is completely backwards compatible with the previous Rev 1.3 spec.
The HDMI Rev 1.4 cable without Ethernet uses the same connector and wires we have used from the days of Rev. 1.0. The connector and cable has 19 pins and wires that are laid out like this:
- 8 wires are used for the balanced TMDS (Transition Minimized Differential Signaling) video
- 2 wires are used for DDC (Digital Display Channel), which carries EDID (Extended Display Identification Data) and HDCP (High Definition Content Protection)
- 1 wire is used for the 5-volt power line
- 1 wire is used for the HotPlug Detect signal
- 1 wire is used for the CEC (Consumer Electronic Control)
- 1 wire was left undefined, open for future use
Add them up and you get 13 wires out of the original 19 that are used as actually signal-carrying wires with an extra for future use. The balance of the 19 wires are used to ground these channels individually and many times wired in a common ground configuration.
In the case of HDMI 1.4 with Ethernet - now known as HEAC (HDMI, Ethernet, Audio, Control) - the wire scheme is exactly the same except for one change: the wire used for HotPlug Detect and the unused, undefined wire are now used for Ethernet and the Audio Return Channel. Under HEAC, this pair is balanced and should be twisted with a shield. Although it is not mandatory for cable makers to provide this modification to the cable, without it cables will likely fail HDMI compliance and DPL Certification.
Yep, HDMI was able to use the HotPlug Detect wire for two jobs, one being HotPlug detection and the other to support the opposite polarity of the balanced line for Ethernet and the Audio Return Channel. As far as system sources (such as Blu-ray players) and display devices (such as flat panels) are concerned, nothing has changed; the cables really “look” the same. Neat trick!
So does this mean you can ignore Rev. 1.4 and skip merrily along your way? Not quite! Longer term technology trends must be addressed in your system design. I will cover this part of the story in a future column.
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