Mobile High-Definition Link (MHL) is an

industry standard ''Industry Standard'' is the sixth studio album by the Dixie Dregs, released in 1982. This was the second of two albums released under the moniker The Dregs, and is their only album featuring vocals (by Alex Ligertwood of Santana and Patrick Si ...

for a mobile audio/video interface that allows the connection of

smartphone A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whic ...

s, tablets, and other portable

consumer electronics Consumer electronics or home electronics are electronic (analog or digital) equipment intended for everyday use, typically in private homes. Consumer electronics include devices used for entertainment, communications and recreation. Usually r ...

devices to

high-definition television High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the g ...

s (HDTVs), audio receivers, and projectors. The standard was designed to share existing mobile device connectors, such as

Micro-USB The initial versions of the USB standard specified connectors that were easy to use and that would have acceptable life spans; revisions of the standard added smaller connectors useful for compact portable devices. Higher-speed development of t ...

, and avoid the need to add additional video connectors on devices with limited space for them. MHL connects to display devices either directly through special

HDMI High-Definition Multimedia Interface (HDMI) is a proprietary audio/video interface for transmitting uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controller, ...

inputs that are MHL-enabled, or indirectly through standard HDMI inputs using MHL-to-HDMI adapters. MHL was developed by a

consortium A consortium (plural: consortia) is an association of two or more individuals, companies, organizations or governments (or any combination of these entities) with the objective of participating in a common activity or pooling their resources for ...

of five companies:

Nokia Nokia Corporation (natively Nokia Oyj, referred to as Nokia) is a Finnish multinational corporation, multinational telecommunications industry, telecommunications, technology company, information technology, and consumer electronics corporatio ...

Samsung The Samsung Group (or simply Samsung) ( ko, 삼성 ) is a South Korean multinational manufacturing conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affiliated businesses, most of them united under the ...

Silicon Image Silicon Image is a provider of semiconductors for the mobile, consumer electronics and personal computers (PCs). It also manufactures wireless and wired connectivity products used for high-definition content. The company’s semiconductor and IP p ...

Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...

and

Toshiba , commonly known as Toshiba and stylized as TOSHIBA, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. Its diversified products and services include power, industrial and social infrastructure system ...

History

Silicon Image, one of the founding companies of the

standard, originally demonstrated a mobile

interconnect In telecommunications, interconnection is the physical linking of a carrier's network with equipment or facilities not belonging to that network. The term may refer to a connection between a carrier's facilities and the equipment belonging to ...

at the January 2008

Consumer Electronics Show CES (; formerly an initialism for Consumer Electronics Show) is an annual trade show organized by the Consumer Technology Association (CTA). Held in January at the Las Vegas Convention Center in Winchester, Nevada, United States, the event typ ...

(CES), based on its

transition-minimized differential signaling Transition-minimized differential signaling (TMDS), a technology for transmitting high-speed serial data, is used by the DVI and HDMI video interfaces, as well as by other digital communication interfaces. The transmitter incorporates an advan ...

(TMDS) technology. This interface was termed "Mobile High Definition Link" at the time of the demonstration, and is a direct precursor of the implementation announced by the MHL Consortium. The company is quoted as saying it did not ship that original technology in any volume, but used it as a way to get a

working group A working group, or working party, is a group of experts working together to achieve specified goals. The groups are domain-specific and focus on discussion or activity around a specific subject area. The term can sometimes refer to an interdis ...

started. The working group was announced in September 2009, and the MHL Consortium founded in April 2010 by

and

. The MHL specification version 1.0 was released in June 2010, and the Compliance Test Specification (CTS) was released in December 2010. May 2011 marked the first retail availability of MHL-enabled products. The first mobile device to feature the MHL standard was the

Samsung Galaxy S II The Samsung Galaxy S II (or Galaxy S2) is a touchscreen-enabled, slate-format Android smartphone designed, developed, and marketed by Samsung Electronics, as the second smartphone of the Samsung Galaxy S series. It has additional software featu ...

, announced at the 2011

Mobile World Congress MWC Barcelona (formerly but still commonly referred to as Mobile World Congress) is an annual trade show organised by GSMA, dedicated primarily to the mobile communications industry. The event is held in Barcelona, Catalonia, Spain at the Fir ...

. MHL announced in 2014 that more than half a billion MHL-capable products had been shipped since the standard was created.

Overview

MHL is an adaptation of

intended for mobile devices such as smartphones and tablets. Unlike

DVI Digital Visual Interface (DVI) is a video display interface developed by the Digital Display Working Group (DDWG). The digital interface is used to connect a video source, such as a video display controller, to a display device, such as a comp ...

, which is compatible with HDMI using only passive cables and adapters, MHL requires that the HDMI socket be MHL-enabled (to deliver an MHL signal to a non-MHL HDMI socket, one can use an adapter device that receives the signal on an MHL-enabled socket, converts it to HDMI, and transmits the HDMI to the non-MHL socket). It has several aspects in common with HDMI, such as the ability to carry uncompressed

HDCP High-bandwidth Digital Content Protection (HDCP) is a form of digital copy protection developed by Intel Corporation to prevent copying of digital audio and video content as it travels across connections. Types of connections include DisplayPort ...

encrypted

high-definition video High-definition video (HD video) is video of higher resolution and quality than standard-definition. While there is no standardized meaning for ''high-definition'', generally any video image with considerably more than 480 vertical scan lines (No ...

, eight-channel

surround sound Surround sound is a technique for enriching the fidelity and depth of sound reproduction by using multiple audio channels from speakers that surround the listener ( surround channels). Its first application was in movie theaters. Prior to sur ...

, and control remote devices with

Consumer Electronics Control Consumer Electronics Control (CEC) is a feature of HDMI designed to control HDMI connected devices by using only one remote controller; so, individual CEC enabled devices can command and control each other without user intervention, for up to 15 de ...

(CEC). There are a total of five pins used in MHL rather than the 19 used in HDMI, namely: a differential pair for data, a bi-directional control channel (CBUS), power charging supply, and ground. This permits a much lighter cable and a much smaller connector on the mobile device, as a typical MHL source will be shared with USB 2.0 on a standard 5-pin

receptacle. (Although MHL ports can be dedicated to MHL alone, the standard is designed to permit port sharing with the most commonly used ports.) The USB port switches from USB to MHL when it recognizes an MHL-qualified sink (e.g., a TV) detected on the control wire. A typical MHL sink will be shared with HDMI on a standard 19-pin HDMI receptacle. Because the same five-pin Micro-USB port is also typically used for charging the device, the sink is required to provide power to maintain the state of charge (or even recharge) while it is being used (although this is dependent on the power available being sufficient e.g., MHL 2 & 3 provide a minimum of 4.5 W / 900 mA, while superMHL can provide up to 40 W). The use of the power line in this way differs from HDMI, which expects the source to provide 55 mA for the purpose of reading the

EDID Extended Display Identification Data (EDID) and Enhanced EDID (E-EDID) are metadata formats for display devices to describe their capabilities to a video source (e.g. graphics card or set-top box). The data format is defined by a standard published ...

of a display. Because of to the low pin count of MHL versus HDMI, the functions that are carried on separate dedicated pins on HDMI, namely: the

Display Data Channel The Display Data Channel, or DDC, is a collection of protocols for digital communication between a computer display and a graphics adapter that enable the display to communicate its supported display modes to the adapter and that enable the com ...

(DDC) (pins 15 & 16) and CEC (pin 13) are instead carried on the bi-directional control bus (CBUS). The CBUS both emulates the function of the DDC bus and also carries an MHL sideband channel (MSC), which emulates the CEC bus function, and allows a TV remote to control the media player on a phone with its Remote Control Protocol (RCP).

Bandwidth

MHL uses the same

Transition-minimized differential signaling Transition-minimized differential signaling (TMDS), a technology for transmitting high-speed serial data, is used by the DVI and HDMI video interfaces, as well as by other digital communication interfaces. The transmitter incorporates an advan ...

(TMDS) as HDMI to carry video, audio, and auxiliary data. However, MHL differs from HDMI in that there is only one differential pair to carry the TMDS data lane, compared to HDMI's four (three data lanes, plus the clock). Therefore these three logical data channels are instead time-division multiplexed into the single physical MHL data lane (i.e., with the logical channels sent sequentially), and the clock signal carried as a common mode signal of this pair. From MHL 3 onwards, the method for carrying the clock signal changed to being carried separately on the MHL CBUS pin instead. The normal (24 bit) mode operates at 2.25 Gbit/s, and multiplexes the same three channel, 24 bit color signal as HDMI, at a pixel clock rate of up to 75 MHz, sufficient for

1080i 1080i (also known as Full HD or BT.709) is a combination of frame resolution and scan type. 1080i is used in high-definition television (HDTV) and high-definition video. The number "1080" refers to the number of horizontal lines on the screen. ...

and

720p 720p (1280×720 px; also called HD ready, standard HD or just HD) is a progressive HDTV signal format with 720 horizontal lines/1280 columns and an aspect ratio (AR) of 16:9, normally known as widescreen HDTV (1.78:1). All major HDTV broadcast ...

at 60 Hz. One period of the MHL clock equals one period of the pixel clock, and each period of the MHL clock transmits three 10-bit TMDS characters (i.e., a 24-bit pixel, where each 10-bit TMDS character represents an encoded byte – 8-bits). MHL can also operate in PackedPixel mode at 3 Gbit/s, catering for

1080p 1080p (1920×1080 progressively displayed pixels; also known as Full HD or FHD, and BT.709) is a set of HDTV high-definition video modes characterized by 1,920 pixels displayed across the screen horizontally and 1,080 pixels down the screen vert ...

, in this case only two channels are multiplexed, as the color signal is changed to a chroma subsampled (YCbCr 4:2:2) pair of adjacent 16-bit pixels (i.e., where two adjacent pixels share chroma values and are represented with only 36-bits), and the pixel clock is doubled to 150 MHz. In this mode, one clock period of the MHL clock now equals two periods of the pixel clock, so each period of the MHL clock transmits twice the number of channels i.e., four 10-bit TMDS characters (a pair of 16-bit pixels). Version 3 of MHL changed from being frame-based to a packet-based technology, and operates at 6 Gbit/s. superMHL extends this by carrying the data signal over more than one differential pair (up to four with USB Type-C, or a total of six using a superMHL cable) allowing up to 36 Gbit/s.

Versions

All MHL specifications are backward compatible to previous versions of the standard. MHL is connection agnostic (i.e., not tied to a specific type of hardware connector). The first implementations used the 5-pin MHL-USB connector described below, and all are supported over USB Type-C MHL Alternate Mode. Other proprietary and custom connections are also allowed.

MHL 1

Version 1.0 was introduced in June 2010, supporting uncompressed HD video up to 720p/1080i 60 Hz (with RGB and YCbCr 4:2:2/4:4:4 pixel encoding). Support for

60 Hz (YCbCr 4:2:2) was introduced in version 1.3. The specification supports standard SD (

Rec. 601 ITU-R Recommendation BT.601, more commonly known by the abbreviations Rec. 601 or BT.601 (or its former name CCIR 601) is a standard originally issued in 1982 by the CCIR (an organization, which has since been renamed as the Internatio ...

) and HD (

Rec. 709 Rec. 709, also known as Rec.709, BT.709, and ITU 709, is a standard developed by ITU-R for image encoding and signal characteristics of high-definition television. The most recent version is BT.709-6 released in 2015. BT.709-6 defines the P ...

) color spaces, as well as those introduced in HDMI 1.3 and 1.4 (

xvYCC xvYCC or extended-gamut YCbCr is a color space that can be used in the video electronics of television sets to support a gamut 1.8 times as large as that of the sRGB color space. xvYCC was proposed by Sony, specified by the IEC in October 2005 an ...

, sYCC601,

Adobe RGB The Adobe RGB (1998) color space or opRGB is a color space developed by Adobe Systems, Inc. in 1998. It was designed to encompass most of the colors achievable on CMYK color printers, but by using RGB primary colors on a device such as a compu ...

, and AdobeYCC601). Other features include 192 kHz 24-bit

LPCM Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amp ...

8-channel

audio,

1.4 content protection, and a minimum of 2.5 W (500 mA) power between sink (e.g., TV) and source (e.g., mobile phone) for charging. The MHL sideband channel (MSC) includes a built-in Remote Control Protocol (RCP) function allowing the

remote control In electronics, a remote control (also known as a remote or clicker) is an electronic device used to operate another device from a distance, usually wirelessly. In consumer electronics, a remote control can be used to operate devices such as ...

of the TV to operate the MHL mobile device through TV's

(CEC) function, or allowing a mobile device to manage the playback of its content on the TV.

MHL 2

Version 2.0 was introduced in April 2012, and raised the minimum charging supply to 4.5 W (900 mA), with an optional 7.5 W (1.5 A) maximum allowed. Support for 3D video was also introduced, permitting 720p/1080i 60 Hz, and 1080p 24 Hz 3D video modes. The specification also included additional MHL sideband channel (MSC) commands.

MHL 3

Version 3.0 was introduced in August 2013, and added support for 4K Ultra HD (3840 × 2160) 30 Hz video, increasing the maximum bandwidth from 3 Gbit/s to 6 Gbit/s. An additional YCbCr 4:2:0 pixel encoding for 4K resolution was also introduced, while the maximum charging supply was increased to 10 W (2 A). Support for compressed lossless audio formats was added with support for

Dolby TrueHD Dolby TrueHD is a lossless, multi-channel audio codec developed by Dolby Laboratories for home video, used principally in Blu-ray Disc and compatible hardware. Dolby TrueHD, along with Dolby Digital Plus (E-AC-3) and Dolby AC-4, is one of the int ...

and

DTS-HD Master Audio DTS-HD Master Audio (DTS-HD MA; known as DTS++ before 2004) is a multi-channel, lossless audio codec developed by DTS as an extension of the lossy DTS Coherent Acoustics codec (DTS CA; usually itself referred to as just DTS). Rather than being ...

. The specification increased the speed of the bi-directional data channel from 1 Mbit/s to 75 Mbit/s to enable concurrent 4K video and

human interface device A human interface device or HID is a type of computer device usually used by humans that takes input from humans and gives output to humans. The term "HID" most commonly refers to the USB-HID specification. The term was coined by Mike Van Fl ...

(HID) support, such as mice, keyboards, touchscreens, and game controllers. Other features include support for simultaneous multiple displays, improved Remote Control Protocol (RCP) with new commands, and HDCP 2.2 content protection.

superMHL

superMHL 1.0 was introduced in January 2015, supporting 8K Ultra HD (7680 × 4320) 120 Hz High Dynamic Range (HDR) video with wide color gamut ( Rec. 2020) and 48-bit deep color. Support for object-based audio formats were added, such as

Dolby Atmos Dolby Atmos is a surround sound technology developed by Dolby Laboratories. It expands on existing surround sound systems by adding height channels, allowing sounds to be interpreted as three-dimensional objects with neither horizontal, nor verti ...

and DTS:X, with an audio-only mode also available. The Remote Control Protocol (RCP) was also extended to link multiple MHL devices together (e.g., TV, AVR, Blu-ray Disc player) and control them via one remote. The specification introduces a reversible 32-pin superMHL connector, which (along with USB Type-C) supports a higher charging power of up to 40 W (20 V / 2 A), and is designed for future bandwidth expansion. The increase in bandwidth over previous MHL versions is achieved by using multiple A/V lanes, each operating at 6 Gbit/s, with a maximum of six A/V lanes supported depending on device and connector type. For example, Micro-USB and HDMI Type-A support one A/V lane, USB Type-C supports up to four A/V lanes, and the superMHL connector supports up to six A/V lanes (36 Gbit/s). In addition to supporting a variable number of lanes, the specification supports

VESA VESA (), formally known as Video Electronics Standards Association, is an American technical standards organization for computer display standards. The organization was incorporated in California in July 1989To retrieve the information, searc ...

Display Stream Compression DisplayPort (DP) is a digital display interface developed by a consortium of PC and chip manufacturers and standardized by the Video Electronics Standards Association (VESA). It is primarily used to connect a video source to a display device su ...

(DSC) 1.1, a "visually lossless" (but mathematically lossy) video compression standard. In cases when the bandwidth of the available lane(s) is unable to meet the rate of the uncompressed video stream, bandwidth savings of up to 3:1 can be achieved with a DSC compression rate of 3.0×. For example, 4K 60 Hz is possible using a single lane (e.g., Micro-USB / HDMI Type-A) with a DSC rate of 3.0×. superMHL can use a variety of source and sink connectors with certain limitations: micro-USB or proprietary connectors can be used for the source only, HDMI Type-A for the sink only, while the USB Type-C and the superMHL connectors can be used for the source or sink.

Connectors

Micro-USB-to-HDMI (five-pin)

The first implementations use the most common mobile connection (

) and the most common TV connection (

). There are two types of connection, depending on whether the display device directly supports MHL.

Passive cable

Passive cables allow MHL devices to connect directly to MHL-enabled TVs (i.e. display devices or AV receivers with an MHL-enabled HDMI port) while providing charging power upstream to the mobile device. Other than the physical connectors, no USB or HDMI technology is being used. Exclusively MHL signaling is used through the connectors and over the cable.

Active adapter

With an active adapter, MHL devices are able to connect to HDMI display devices that do not have MHL capability by actively converting the signal to HDMI. These adapters often feature an additional Micro-USB port on them to provide charging power to the mobile device because standard HDMI ports do not supply sufficient current.

Samsung Micro-USB-to-HDMI adapter and tip (eleven-pin)

The

Samsung Galaxy S III The Samsung Galaxy S III (or Galaxy S3) is an Android smartphone designed, developed, and marketed by Samsung Electronics. Launched in 2012, it had sold more than 80 million units overall, making it the most sold phone in the S series. I ...

, and later

Galaxy Note II The Samsung Galaxy Note II (or Galaxy Note 2) is an Android phablet smartphone. Unveiled on August 29, 2012 and released in October 2012, the Galaxy Note II is a successor to the original Galaxy Note, incorporating improved stylus functionality ...

and

Galaxy S4 The Samsung Galaxy S4 is an Android smartphone produced by Samsung Electronics as the fourth smartphone of the Samsung Galaxy S series and was first shown publicly on March 14, 2013, at Samsung Mobile Unpacked in New York City. It is the succes ...

, use an 11-pin connector and the six additional connector pins in order to achieve functional improvements over the 5-pin design (like simultaneous USB-OTG use). However, if consumers have a standard MHL-to-HDMI adapter all they need to purchase is a tip. With the launch of the Samsung Galaxy S4, Samsung also released MHL 2.0 smart adapter with a built-in 11-pin connector. The first Samsung MHL 1.0 smart adapter released with the Galaxy S III requires external power and is able to work with HDMI TVs at 1080p at 24 Hz. The MHL 2.0 adapter released with the Galaxy S4 can output 1080p at 60 Hz and does not need external power.

USB Type-C (MHL Alternate Mode)

The MHL Alternate Mode for

USB 3.1 USB 3.0, released in November 2008, is the third major version of the Universal Serial Bus (USB) standard for interfacing computers and electronic devices. Among other improvements, USB 3.0 adds the new transfer rate referred to as '' ...

specification allows MHL enabled source and display devices to be connected through a USB Type-C port. The standard was released on November 17, 2014, and is backward compatible with existing MHL specifications: supporting MHL 1, 2, 3 and superMHL. The standard supports the simultaneous transfer of data (at least

USB 2.0 Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...

, and depending on video resolution:

Gen 1 or 2) and power charging (up to 40 W via

USB Power Delivery The initial versions of the USB standard specified connectors that were easy to use and that would have acceptable life spans; revisions of the standard added smaller connectors useful for compact portable devices. Higher-speed development of t ...

), in addition to MHL audio/video. This allows the connection to be used with mobile/laptop docks, allowing devices to connect to other peripherals while charging. The use of passive cables is possible when both devices support the standard, e.g., when connecting to superMHL, USB Type-C, and MHL-enabled HDMI, otherwise, an active cable adapter is necessary to connect to standard HDMI devices. Depending on the bandwidth requirement, the standard makes use of a variable number of USB Type-C's four SuperSpeed differential pairs to carry each

TMDS Transition-minimized differential signaling (TMDS), a technology for transmitting high-speed serial data, is used by the DVI and HDMI video interfaces, as well as by other digital communication interfaces. The transmitter incorporates an advan ...

lane: a single lane is required for resolutions up to 4K/60 Hz, two lanes for 4K/120 Hz, and all four lanes for 8K/60 Hz. The MHL eCBUS signal is sent over a side-band (SBU) pin on the USB Type-C connector. When one or two lanes are used, USB 3.1 data transfer is supported. MHL Alt Mode - USB Type-C pin mapping

In common MHL Alt Mode implementations on mobile/tablet/laptops, the video from the

GPU A graphics processing unit (GPU) is a specialized electronic circuit designed to manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device. GPUs are used in embedded systems, mobi ...

will be converted to MHL signal by using a MHL transmitter chip. The transmitter chips often accept video in MIPI ( DSI/

DPI A Daytona Prototype International (DPi) was a type of sports prototype racing car developed specifically for the International Motor Sports Association's WeatherTech SportsCar Championship, as their top class of car, acting as a direct replaceme ...

) or

format and convert it to MHL format. The USB Type-C port controller functions as a switch/mux, passing through the MHL signal to the external devices. The dock/display devices may use an MHL bridge chip to convert the MHL signal to HDMI signal format.

superMHL (32-pin)

In conjunction with the release of the superMHL specification in January 2015, MHL introduced a reversible 32-pin superMHL connector. The connector can carry six A/V lanes over six differential pairs, catering for the full 36 Gbit/s bandwidth available from the superMHL standard. The connector also enables 40 W of charging power at a higher voltage and current.

Comparison with SlimPort / Mobility DisplayPort (MyDP)

SlimPort DisplayPort (DP) is a digital display interface developed by a consortium of PC and chip manufacturers and standardized by the Video Electronics Standards Association (VESA). It is primarily used to connect a video source to a display device su ...

is a proprietary alternative to MHL, based on the

DisplayPort DisplayPort (DP) is a digital display interface developed by a consortium of PC and chip manufacturers and standardized by the Video Electronics Standards Association (VESA). It is primarily used to connect a video source to a display device su ...

standard integrated into common microUSB ports and supports up to 1080p60 or 1080p30 with 3D content over HDMI 1.4 (up to 5.4 Gbit/s of bandwidth), in addition to support for DVI, VGA (up to 1920 x 1080 at 60 Hz), and DisplayPort.

References

External links

* {{High-definition Computer-related introductions in 2008 Computer-related introductions in 2010 Digital display connectors Film and video technology High-definition television Standards Television technology Ultra-high-definition television Serial buses