DisplayPort has made a few timid steps
forward since its 2006 introduction; but based on what we saw at CES in
January, 2012 might be the year it finally breaks through to mainstream usage.
VESA [the Video Electronics Standards
Association) designed DisplayPort to be a royalty free means of delivering
digital audio and video signals from a source device to a display. As such, it
was intended to allow the retirement of both DVI (the Digital Visual Interface)
and VGA (Video Graphics Array), which outlived its usefulness shortly after DVI
appeared on the scene. DisplayPort can be used to connect computers to desktop
monitors and televisions, as well as internally (in a laptop or all-in-one
computer, for instance).
DisplayPort
1.2
Displayport versions
The original specification supported a
maximum data rate of 8.64Gb/s on a two meter copper cable. In 2007, DisplayPort
1.1a added support for fiber optic cable, which can carry signals more than 15
meters without developing ghosting or other signal-degradation problems.
Version 1.1a also added support for the DRM systems HDCP (commonly used in
consumer electronics gear) and DPCP (DisplayPort Content Protection).
DisplayPort 1.2, introduced in 2009,
doubled effective bandwidth to 17.28Gb/s, rendering the standard capable of
delivering higher resolutions and refresh rates, as well as increased color
depth. DisplayPort 1.2 can also carry multiple independent video streams (to
support multiple monitors in a daisy-chain fashion), and it supports
stereoscopic 3D. This version increased auxiliary channel bandwidth to a
maximum of 720Mb/s (for device management and control, including the
bi-directional carriage of USB signals); expanded color spaces to include
xvYCC, scRGB, and Adobe RGB 1998; and added support for Global Time Code (GTC),
to enable sub-1-microsecond audio/ video synchronization.
Aside from its USB capability, DisplayPort
1.2 sounds a lot like HDMI, doesn't it? Craig Wiley, chairman of the VESA board
of directors, begs to differ. "Today, DisplayPort and HDMI really address
two different markets. What is important to TV manufacturers isn't to PC
manufacturers, and vice versa. Because of this, we do believe the two standards
will coexist as external interfaces for the foreseeable future. That being said,
Embedded DisplayPort and MYDP Mobility DisplayPort, an improved version of the
DisplayPort standard for mobile devices provide additional avenues for
DisplayPort to gain adoption. As devices trend toward smaller form factors and
become more mobile, we see this as a major growth opportunity for us."
VESA showed several prototype Mobility
DisplayPort devices at CES. MYDP is designed to simplify the process of
streaming audio and video from a mobile device to a large display without
adding another port to the mobile device. It accomplishes this trick by sending
high-definition video out the device's Micro USB port to a cable equipped with
a USB plug on one end and a DisplayPort, HDMI, or VGA plug on the other. The
new standard will also allow video conference calls by tapping into the camera
on your phone or tablet.
Unfortunately, this requires a chip on the
sending device that switches between DisplayPort mode and USB mode, so it won't
be possible to retrofit your existing phone or tablet. No changes are required
at the display end, however, and the device's battery can be charged at the
same time (the DisplayPort 1.2a spec will boost power output from a current 1.5
watts to 9 watts).
How displayport works
DisplayPort uses a self-clocking
packet-based communications protocol, similar to what's used in Ethernet, USB,
and PCI Express. This packet approach renders DisplayPort extensible; i.e., new
features can be added without requiring significant changes to the physical interface.
A DisplayPort connector supports one, two, or four differential data pairs (aka
lanes] in a main link. Each lane has a raw bitrate of 1.62-, 2.7-, or 5.4Gb/s,
clocked at 162-, 270-, or 540MHz. Data is 8b/10b encoded, meaning that every
eight bits of information is encoded with a 10-bit symbol to achieve an
effective (post-decoding) data rate of 1.296-, 2.16-, or 4.32Gb/s per lane [80
percent of the raw bitrate).
You might be surprised to learn that the
DisplayPort spec treats both audio and video signals as optional. A DisplayPort
cable might carry only audio content, only video content, or both audio and
video simultaneously. DisplayPort's video signal path supports 6-16 bits per
color channel, and the audio path can carry up to eight channels of
uncompressed linear PCM audio encoded at resolutions of 16-24 bits and at
sampling rates of 32-192kHz.
A 720Mb/s, bi-directional, half-duplex
auxiliary channel on DisplayPort's main link provides device management and
control. It supports communications protocols such as EDID (Extended Display
Identification Data], DPMS (Display Power Management Signal- ng], and MCCS
(Monitor Command Control Set] that enable a display to inform its host of its
capabilities and the host to manage the display's settings and power state.
Unlike HDMI, DisplayPort does not support AV.link, a low-bandwidth
command-and-control protocol common in the consumer-elec-tronics industry.
AV.link enables the host to send remote-control commands to the client. HDMI
uses CEC (Consumer Electronics Control) to carry AV.link data on a single wire,
so DisplayPort's aux channel could conceivably be used for this same purpose.
Dual-mode DisplayPort chipsets are capable
of emitting single-link HDMI and DVI signals with the connection of the appropriate
passive adapter. The chip-set detects the presence of the adapter and
automatically switches to DVI/HDMI mode. Dual-mode ports, which are present on
most DisplayPort-compatible videocards and displays, are marked with a DP++
logo. An active adapter is required to support dual-link DVI and analog
component video devices (including VGA], due to DisplayPort's limited pin
count.
Prospects
VESA hasn't delivered the long ball every
time it has come up to bat, so there's no guarantee that DisplayPort 1.2 will
achieve the prominence VESA is hoping for. Two things do stand in its favor:
First, the demand for multiple-display technology is on the rise, thanks in
large measure to gamers (especially flight-sim fans] and businesses (especially
in the financial sector, where stock tickers, spreadsheets, and other analysis
software all run simultaneously). DisplayPort delivers a much better
multi-display solution than HDMI is currently capable of delivering.
The second factor in DisplayPort's favor is
that it's not absolutely necessary to purchase a brand-new monitor in order to
utilize it, thanks to the availability of DVI and VGA adapters. Bells and
whistles will attract early adopters to almost any new technology, but only a
solid return on investment will ensure its long-term viability. With innovative
new features, backward compatibility, and reduced manufacturing costs,
DisplayPort is finally showing it has legs.
DisplayPort 1.2 Pin Out
Here's what's happening behind the scenes
of an external source-side connector. The spec's packet-based approach makes it
possible to add new features without significantly changing the physical
interface.
Pin 1 ML_Lane 0 (p) Lane
0 (positive)
Pin 2 GND Ground
Pin 3 ML_Lane 0 (n) Lane
0 (negative)
Pin 4 Ml__Lane 1 (p) Lane
1 (positive)
Pin 5 GND Ground
Pin 6 ML_Lane 1 (n) Lane
0 (negative)
Pin 7 ML_Lane 2 (p) Lane
2 (positive)
Pin 8 GND Ground
Pin 9 Ml__Lane 2 (n) Lane
2 (negative)
Pin 10 ML_Lane 3 (p) Lane
3 (positive)
Pin 11 GND Ground
Pin 12 ML_Lane 3 (n) Lane
3 (negative)
Pin 13 C0NFIG1 Connected
to Ground
Pin 14 C0NFIG2 Connected
to Ground
Pin 15 AUX CH (p) Auxiliary
Channel (positive)
Pin 16 GND Ground
Pin 17 AUX CH (p) Auxiliary
Channel (negative)
Pin 18 Hot Plug Hot
Plug Defect
Pin 19 Return Return
for Power
Pin 20 DP_PWR Power for
Connector (3.3 V 500 mA)
