DisplayPort

DisplayPort is a universal, license-free connection standard for the transmission of digital video and audio signals, standardized by the Video Electronics Standards Association (VESA) . The main area of application is the connection of computer monitors to PCs or notebooks.

Locking DisplayPort connector

Video outputs of a graphics card: at the top right a DVI socket,
at the bottom three DisplayPort and an HDMI socket (second from the left)

motivation

DisplayPort was originally designed to accelerate the transition to digital interfaces, which are a prerequisite for higher display quality. The connection also takes up less space than VGA and DVI and is therefore better suited for portable devices such as notebooks . In contrast to the competing HDMI connector, the plug connection is mechanically locked using two resilient barbs that are released by pressing a button on the connector housing.

Technically sets DisplayPort to a main connection ( English Main Link ) consisting of one, two, or four lanes (lane 0 to lane 3) with high bandwidth, low latency , which allows a data flow in one direction only. Version 1.0 supports a video stream including audio.

DisplayPort 1.0 includes an additional channel (AUX channel, English auxiliary ), which allows a bidirectional connection with low latencies and constant bandwidth in order to control devices according to the VESA standards E- DDC , E- EDID , DDC / CI and MCCS enable. This makes real plug and play possible. The AUX channel can be used for various purposes, including consumer electronics control or USB .

development

DisplayPort logo

The first DisplayPort specification was published on May 1, 2006.

Revision 1.1a was published on January 11, 2007, initially containing mainly corrections. In April 2007, the VESA passed the final version 1.1, which includes support for encryption using HDCP 1.3. This copy protection ( DRM ) is already used with DVI and HDMI . In addition to HDCP, DPCP (DisplayPort Content Protection) is also supported.

Version 1.2 was published on December 22nd, 2010, innovations include support for Multi Stream Transport (MST), stereoscopy (“3D”), the xvYCC , scRGB and Adobe RGB 1998 color spaces . In addition, the data rate of the AUX channel was increased from 1 Mbit / s to 720 Mbit / s, which allows applications with higher bandwidth requirements. In addition, the DisplayPort specification from version 1.2 is no longer freely available, but can only be viewed against payment or (also chargeable) membership in the VESA group.

Version 2.0 was released on June 26, 2019.

Pin assignment

The table shows the pin assignment of a DisplayPort video source (PC, laptop). On the monitor side, lanes 0 to 3 are crossed, i.e. H. Lane 0 is connected to Lane 3, Lane 1 to Lane 2 on the opposite side.

Pin assignment DisplayPort connector (PC side)

Pin code	signal	Pin code	signal
01	LVDS - line 0+
01	LVDS - line 0+	02	Dimensions
03	LVDS line 0−	02	Dimensions
03	LVDS line 0−	04th	LVDS - line 1+
05	Dimensions	04th	LVDS - line 1+
05	Dimensions	06th	LVDS - line 1−
07th	LVDS - line 2+	06th	LVDS - line 1−
07th	LVDS - line 2+	08th	Dimensions
09	LVDS - line 2−	08th	Dimensions
09	LVDS - line 2−	10	LVDS - line 3+
11	Dimensions	10	LVDS - line 3+
11	Dimensions	12	LVDS - line 3−
13	Config 1	12	LVDS - line 3−
13	Config 1	14th	Config 2
15th	AUX channel +	14th	Config 2
15th	AUX channel +	16	Dimensions
17th	AUX channel -	16	Dimensions
17th	AUX channel -	18th	Hot-plug detection
19th	Power supply: ground	18th	Hot-plug detection
19th	Power supply: ground	20th	Power supply: +3.3 V / 0.5 A.
		20th	Power supply: +3.3 V / 0.5 A.

Further developments

DisplayPort 1.1

Dual-mode DisplayPort

DisplayPort 1.1, also known under the names Dual-mode DisplayPort and DisplayPort ++ , allows compatibility with DVI and HDMI, so that a connection is possible using inexpensive adapters that only have to adapt the electrical signaling level from TMDS to LVDS . The graphics chip manufacturers Intel , AMD and Nvidia achieve this with a trick that is already applied to the graphics card and not just behind the actual output: If the graphics card detects that the connected device is a model with DisplayPort, the signals are also sent in output in this format. If, however, z. If, for example, an adapter to HDMI is used, this signals the card to switch internally to the HDMI protocol. The adaptation of the different signal levels and impedances of the signaling methods LVDS (DisplayPort) and TMDS (DVI / HDMI) on the electrical level then takes place in the downstream impedance converter / level shifter, which passes the signal edges through unchanged, but adjusts the signal level and impedance to the target interface. However, this support is optional, so the support for the individual connections depends on the manufacturer. You can also connect dual-link DVI and analog VGA , technically it works exactly the same as when connecting an HDMI device. DVI uses the same signal as HDMI, while the graphics card has to generate an analog signal for VGA. If the graphics card does not support this method or only supports a limited number of connections, a so-called active DisplayPort adapter is required (also known as an adapter with Eyefinity support).

The following table summarizes the switching of the contacts on the display port in dual-mode DisplayPort:

Dual-mode contact assignment
DisplayPort contact	DVI 1.0 / HDMI mode
LVDS line 0	TMDS channel 2
LVDS line 1	TMDS channel 1
LVDS line 2	TMDS channel 0
LVDS line 3	TMDS clock
AUX channel +	DDC cycle
AUX channel -	DDC data
Hot plug detection	Hot plug detection
Config 1	DVI / HDMI cable adapter detection
Config 2	Consumer Electronics Control (CEC), only with HDMI

DisplayPort 1.2

DisplayPort 1.2 was introduced on December 22, 2009. The main improvement was the doubling of the data rate from 270 MByte / s to 540 MByte / s per lane for the display of higher resolutions. Another new feature is the possibility of connecting several monitors according to the daisy chain principle , which can be controlled independently of one another. For this function, known as Multi-Stream-Transport (MST), with regard to the series connection of monitors, each relaying monitor requires a DisplayPort-Out socket. This function is discussed in more detail in the Multi-Stream Transport chapter .

DisplayPort 1.3

Compared to DisplayPort 1.2, DisplayPort 1.3 increases the maximum data rate by 50 percent to 810 Mbytes / s per lane. This means that up to 25.92 Gbit / s can be transmitted over the four available lanes, which allows a maximum resolution of 5K (5120 × 2880) at 60 fps and 8 bit color depth without compression . In addition, Version 1.3 of the DisplayPort standard includes compression through 4: 2: 0 color subsampling for the first time , so that future UHD 2 displays with a resolution of 8K (7680 × 4320) at 60 fps and 8 bit color depth are supported.

DisplayPort 1.4

DisplayPort 1.4 was released on March 1, 2016. HBR3 with 25.92 Gbit / s still remains as the fastest possible transmission rate, as no new transmission mode has been defined. However, a feature update has been carried out with support for Display Stream Compression 1.2 (DSC) , forward error correction , HDR10 , the Rec. 2020 color space and the extension of the audio channels to 32.

DisplayPort 2.0

DisplayPort 2.0 was released on June 26, 2019. The transmission rate could be increased to 77.37 Gbit / s, which enables a transmission of 8K at 60 Hz with HDR without compression. A 128b / 132b coding is used.

Integrated standards

Display Stream Compression

DSC is a lossy coding with a maximum compression rate of 1: 3. The compression should not be visually visible. With DSC, DisplayPort 1.4 is able to reproduce 8K UHD (7,680 × 4,320 pixels) at 60 Hz and with 10 bit HDR video or 12 bit. For 4K UHD (3840 × 2160 pixels) and 12 bit HDR, frame rates of up to 240 Hz are possible.

Multi-stream transport

Multi-Stream Transport (MST) was introduced with the DisplayPort 1.2 standard. It enables several independent displays to be controlled with a DP port output. Several video streams are multiplexed in the output data stream. MST hubs can split this data stream over several displays. These are often contained in the monitors themselves - recognizable by a DP-Out connection to which another DP monitor can be connected. The protocol supports up to 63 displays, but the cumulative transfer rate is max. that of the standard used (DP 1.2: 17.28 Gbit / s, DP 1.3 / 1.4: 25.92 Gbit / s) is available. In addition, the maximum number of connections between the source and a device (ie the maximum length of a chain) is 7. With the release of the new MST, the standard single-display mode was retrospectively known as "SST" mode (single stream -Transport).

Daisy-chaining is a function that must be specially supported by each intermediate display. Not all DisplayPort 1.2 devices support this. Daisy chaining requires a dedicated DisplayPort output connector on the display. Standard DisplayPort input connectors on most displays cannot be used as daisy chain output. Only the last display in the daisy chain does not have to specifically support the function or have a DP output connection. DisplayPort 1.1 displays can also be connected to MST hubs and be part of a DisplayPort daisy chain if it is the last display in the chain.

The host system software must also support MST for hubs or daisy chains to work. While Microsoft Windows environments fully support this, Apple operating systems currently do not support MST hubs or DisplayPort chaining from macOS 10.13 ("High Sierra").

DisplayPort to DVI and DisplayPort to HDMI adapters / cables may or may not work through an MST output port. The support for this depends on the respective device.

MST is supported by the USB DisplayPort Type-C alternate mode, so standard DisplayPort daisy chains and MST hubs from Type-C sources work with a simple Type-C to DisplayPort adapter.

Mini DisplayPort

Mini DisplayPort on an Apple MacBook (2008)

In October 2008 Apple introduced a smaller, proprietary variant, the Mini DisplayPort , the specifications of which the manufacturer published under a free license in November 2008 in order to promote its distribution. This Mini DisplayPort was adopted in the VESA specification 1.1a in November 2009. In February 2011, Intel and Apple presented a mechanically and electrically backwards compatible with Mini DisplayPort connection design called Thunderbolt . This is no longer a pure monitor connection, but a universal data interface in the form of USB or FireWire .

Comparison with DVI and HDMI

advantages

Based on a micro-packet protocol:
- Allows a simple extension of the standard
Design to support internal "chip-to-chip" communication:
- Can control a display panel directly. This eliminates the need for scaling and control circuits, and cheaper and thinner screens are possible. Latencies are reduced.
- Replacement for internal LVDS connections to notebook panels through a general standardized interface
- Compatible with low voltage signal environment used in 45 nanometer CMOS manufacturing
Supports both RGB and YCbCr encoded formats
Additional channel can be used for touch-sensitive screens, USB connections, cameras, microphones, etc.
Fewer lines with embedded clock signal, thus reduced RFI (radio interference)
Smaller connector with optional locking that does not require a screw connection
Royalty-free, saves manufacturers of small series (e.g. FPGA boards and FPGA Amigas ) the usual HDMI annual fees of up to $ 10,000. Corresponding Displayport to HDMI cables are very common on the market.

disadvantage

no direct electrical compatibility with DVI - however, it can be emulated through automatic detection of the connection type and switching of the line drivers from DisplayPort 1.1.

Data transfer rates

Possible resolutions: The straight lines mark screen resolutions with given aspect ratios, the hyperbolas the theoretical limits of various interconnects

DisplayPort 1.4 (March 1, 2016):

Thanks to the lossy video compression, sufficient for 7,680 × 4,320 pixels

DisplayPort 1.3 (September 15, 2014) with 810 MHz symbol rate (HBR3):

1 line: 810 MByte / s (6.48 GBit / s): sufficient for 2,560 × 1,600 pixels
2 lines: 1620 Mbytes / s (12.96 GBit / s): sufficient for 3,840 × 2,160 pixels
4 lines: 3240 Mbytes / s (25.92 GBit / s): sufficient for 5,120 × 2,880 pixels

DisplayPort 1.2 (August 2009) with 540 MHz symbol rate (HBR2):

1 line: 540 MByte / s (4.32 GBit / s): sufficient for 1,600 × 1,200 or 1,920 × 1,200 pixels
2 lines: 1080 Mbytes / s (8.64 Gbit / s): sufficient for 3,072 × 1,920 or 2,560 × 1,600 pixels
4 lines: 2160 Mbytes / s (17.28 GBit / s): sufficient for 3,840 × 2,400 or 4,096 × 2,560 pixels

DisplayPort 1.1 with 270 MHz symbol rate (HBR):

1 line: 270 Mbytes / s (2.16 GBit / s): sufficient for 1,400 × 1,050 or 1,440 × 900 pixels
2 lines: 540 MByte / s (4.32 GBit / s): sufficient for 1,600 × 1,200 or 1,920 × 1,200 pixels
4 lines: 1080 Mbytes / s (8.64 Gbit / s): sufficient for 3,072 × 1,920 or 2,560 × 1,600 pixels

DisplayPort 1.1 with 162 MHz symbol rate (RBR):

1 line: 162 MByte / s (1.296 GBit / s): sufficient for 1,024 × 768 pixels
2 lines: 324 MByte / s (2.592 GBit / s): sufficient for 1,680 × 1,050 pixels
4 lines: 648 MByte / s (5.184 GBit / s): sufficient for 2,048 × 1,280 pixels

For comparison DVI / HDMI:

3 lines / DVI-D: 495 MByte / s (3.96 GBit / s): sufficient for 1,920 × 1,200 pixels
6 lines / DVI-D: 990 Mbytes / s (7.92 GBit / s): sufficient for 2,560 × 1,600 pixels
3 lines / HDMI 1.0–1.2: 495 Mbytes / s (3.96 GBit / s): sufficient for 1,920 × 1,200 pixels
3 lines / HDMI 1.3+: 1020 MByte / s (8.16 GBit / s): sufficient for 2,560 × 1,600 pixels
3 lines / HDMI 2.0: 1800 MByte / s (14.4 GBit / s): sufficient for 4,096 × 2,160 pixels

Remarks:

All resolution specifications refer to a 60 Hz frame rate and 3 × 8 bit color depth (without sub-sampling).
In the literature, symbol rates are given as bit rates. However, you can only transmit 8 bits ( ANSI-8B10B modulation) with 10 symbols , so this information is incorrect. The same problem can also be found with other interfaces, such as Serial ATA (1.5 / 3 Gbit / s) and HDMI (4.95 / 10.2 Gbit / s), even with the classic RS-232 interface ( 50 bit / s to 115,200 bit / s).

Alternative multimedia interfaces

SDI (Serial Digital Interface) - video image transmission including audio in studios
HD-SDI (High Definition Serial Digital Interface) - video image transmission including audio in studios
DVI (Digital Visual Interface) - first successful digital interface for computer screens without audio (encryption optional), in the DVI-A and DVI-I versions also suitable for analog monitor connection (downwards compatible with VGA)
HDMI (High Definition Multimedia Interface) - extended for video (in addition to image and audio data as well as encryption and alternative video modes), purely digital, including DVI compatibility mode
UDI (Unified Display Interface) - failed digital video standard from Samsung, Intel and Apple, which was supposed to replace VGA
MHL (Mobile High-Definition Link) - HD video and audio interface, optimized for connecting mobile phones and portable devices to HDTVs
HDBaseT - HD video, audio, USB, network and power up to 100 m via network cable