Mobile High Definition Link

History

Silicon Image, one of the founding companies of the HDMI standard, originally demonstrated a mobile interconnect at the January 2008 Consumer Electronics Show (CES), based on its transition-minimized differential signaling (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 started.

The working group was announced in September 2009, and the MHL Consortium founded in April 2010 by Nokia, Samsung, Silicon Image, Sony and Toshiba. The MHL specification version 1.0 was released in June 2010 and May 2011 marked the first retail availability of MHL-enabled products.

An abridged version of the specification was made available for download on April 14, 2010. MHL specification version 1.0 was released in June 2010. The Compliance Test Specification (CTS) was announced on December 21, 2010.

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

Overview

MHL was originally intended for mobile devices such as smartphones and tablets.

High-definition video and eight-channel surround sound.

Encrypted video and audio via High-bandwidth Digital Content Protection (HDCP).

Transition Minimized Differential Signaling (TMDS) for video, audio, and auxiliary data.

5-volt DC power on the cable.

HDMI-CEC control of remote devices.

To better accommodate the needs of mobile devices, MHL differs from HDMI as follows.

Five wires in place of HDMI's nineteen, namely ground, power, control, and a differential pair for data. This permits a much lighter cable and a much smaller connector on the mobile device.

Whereas HDMI uses the power line to provide 5 volts from the source at 50 mA (0.25 W) for the purpose of awakening a sleeping sink, MHL uses it to provide that voltage from the sink at 900 mA (4.5 W) to maintain the state of charge of the source. This allows a mobile device with only one port for both charging and MHL to operate indefinitely without exhausting the battery, provided 4.5 W is sufficient. Devices needing more power from the port used for MHL may not be suitable candidates for MHL 2.0; MHL 3.0 raises the power requirement to 2 A (10 W).

Although MHL ports can be dedicated to MHL alone, the standard is designed to permit port sharing with the most commonly used ports.

A typical MHL source will be shared with USB 2.0 on a standard 5-pin micro-usb receptacle, which switches from USB to MHL when it recognizes an MHL-qualified sink detected on the control wire.

A typical MHL sink will be shared with HDMI on a standard 19-pin HDMI receptacle. The standard uses the same pins for power (pin 18) and ground (pins 5, 11, and 17), HDMI's Hot Plug detect (pin 19) for MHL control, and HDMI's Data0 channel (pins 7 and 9) for MHL's data.

Whereas HDMI transmits the three bytes of a pixel in parallel over three physically separate differential pairs along with a fourth pair for a clock, with a separate ground for each pair (pins 1-12), MHL transmits them sequentially over one pair (7 and 9), with the clock added in as a common mode signal to the differential signal. The receiver then has both differential and common mode detection circuits. In MHL 3 and superMHL the clock signal is instead carried separately on an extended CBUS, renamed the enhanced control bus (eCBUS).

Whereas HDMI uses three wires to cater for HDMI-CEC (13), and DDC (15 and 16), MHL controls these functions with a single wire (CBUS).

In normal mode MHL supplies the same 24 bit color signal as HDMI, at a pixel clock rate of up to 75 MHz for MHL 2.0, sufficient for 1080i and 720p. Each of the three bytes is in a 10-bit frame whence at 75 MHz the data channel operates at 2.25 Gbit/s.

MHL 2.0 caters for 1080p with a PackedPixel mode utilizing only the first two of HDMI's three channels. This shrinks each pixel to 16 bits (using YCbCr 4:2:2 chroma subsampling) carried in two 10-bit frames. The pixel clock is doubled to 150 MHz and the data channel then operates at 3 Gbit/s.

MHL's serial signaling makes it incompatible with the three-channel parallel signaling of HDMI and DVI. Hence both ends of an MHL channel must implement the standard in full. In particular an MHL source cannot drive an ordinary HDMI or DVI display, though this limitation is easily overcome with an MHL dongle converting MHL to HDMI. An MHL source must be realized in hardware as the typical 5-pin USB 2.0 port on mobile devices is much too slow at 480 Mbit/s for a software-only implementation.

MHL 1 and MHL 2

The TV provides power to the connected device (5 V DC/500 mA with MHL 1.0, 5 V DC/900 mA with MHL 2.0).

Uses a single, thin cable to connect the mobile device to the TV.

The TV remote will control the connected device with guaranteed mixed manufacturer interoperability (CEC). (Also see Silicon Image's press release about MHL on December 14, 2010). Note: The built-in Remote Control Protocol (RCP) function allows you to use the remote control of the TV to operate the MHL mobile device through TV’s Consumer Electronics Control (CEC) function.

1080p uncompressed HD video.

8 channel uncompressed audio (e.g., 7.1 surround sound).

Supports High-bandwidth Digital Content Protection (HDCP).

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. Other proprietary and custom connections are also allowed.

MHL 3

On August 20, 2013, MHL announced its 3 specification to address the latest consumer requirements for connecting a mobile device to displays, marking major advancements in the areas of audio and video transmission over an MHL link. The first devices to include the specification are the Sony Xperia Tablet Z2 and the Sony Xperia Z2. At Mobile World Congress 2014 Silicon Image demoed MHL 3 powered by its SiI8620 transmitter chip. Features of the MHL 3.0 specification include:

4K (Ultra HD): Support of 4K formats up to 3840 × 2160 at 30 Hz

Simultaneous high-speed data channel

Improved Remote Control Protocol (RCP) with new commands

HID support for peripherals such as a touch screen, keyboard and mouse

Higher power charging up to 10 W

Backward compatible with MHL 1 and MHL 2

Latest HDCP 2.2 content protection

Enhanced 7.1 surround sound with Dolby TrueHD and DTS-HD

Connector agnostic – uses as few as five pins

Support for simultaneous multiple displays

superMHL 1.0

On January 6, 2015, MHL announced the superMHL 1.0 specification, the next-generation of MHL technology for CE and mobile devices. Features of superMHL include:

Delivery of up to 8K 120fps video

Deep Color support up to 48-bit color depths

Wider color gamut to view content the way filmmakers intended

High-Dynamic Range (HDR) support to strike the perfect balance of bright spectral highlights along with shadow details

Immersive surround sound with support for object audio such as Dolby Atmos, DTS:X, 3D audio, and an audio-only mode

Advanced connectivity configurations to link multiple MHL devices together (TV, AVR, Blu-ray player) and control them via one remote

Power charging up to 40W

Content on multiple displays when connecting a single device

Backward compatible with MHL 1, MHL 2 and MHL 3

New reversible superMHL connector

Support for the MHL Alt Mode for the USB Type-C specification

HDCP 2.2

The superMHL standard makes use of one to six A/V lanes with each lane operating at 6Gbit/s. Four connectors have been detailed with their various numbers of A/V lanes supported in the standard:

micro-USB (one A/V lane)

HDMI Type-A (one A/V lane)

USB Type-C (one to four A/V lanes)

superMHL (one to six A/V lanes)

superMHL may also use a variety of source and sink connectors:

micro-USB (Source)

USB Type-C (Source or Sink)

Proprietary connectors (Source)

HDMI Type-A (Sink)

superMHL connector (Source or Sink)

superMHL supports delivery of video up to 8K 120fps using 6 lanes (e.g. superMHL connector), 8K 60fps using 4 lanes (e.g. USB Type-C / superMHL connector) and 4K 60fps using 1 lane (e.g. micro-USB / HDMI Type-A / USB Type-C / superMHL connector). The superMHL standard makes use of VESA's Display Stream Compression (DSC) standard version 1.1 to allow for 2.0x, 2.5x, or 3.0x compression. This allows a superMHL source-to-sink connection to transfer 108Gbit/s of visually lossless (mathematically lossy) data.

The following resolutions and frame rates are supported by the superMHL standard (other resolutions and frame rates may be supported):

720×[email protected]/60 Hz

720×576@50 Hz

1280×720p@50/59.94/60 Hz

1920×1080i@50/59.94/60 Hz

1920×1080p@50/59.94/60 Hz

3840×2160@24/25/30/48/50/60 Hz (4K UHD)

5120×2880@24/25/50/60 Hz (5K UHD)

7680×4320@24/25/30/50/60/120 Hz (8K UHD)

The following pixel encodings and color spaces are supported by the superMHL standard:

RGB 4:4:4 pixel encoding

YCbCr 4:4:4 pixel encoding

YCbCr 4:2:2 pixel encoding

YCbCr 4:2:0 pixel encoding (4K resolution and above)

xvYCC

BT.2020 (8K and 4K UHD)

Rec.709

sYCC601

AdobeYCC601

AdobeRGB

The superMHL connector is considered to be more futuristic than the HDMI or DisplayPort connectors. superMHL connector supports more A/V lanes, it has more pins and it is reversible (like USB Type-C). superMHL connector supports future bandwidth expansion and it can deliver more power than other connectors. While USB Type-C is considered to be a small form factor connector, the superMHL connector has a form factor comparable to HDMI Type-A connector.

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

The first implementations use the most common mobile connection (Micro-USB) and the most common TV connection (HDMI). There are two types of connection, depending 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, and later Galaxy Note II and Galaxy S4, 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 a Samsung 2.0 smart adapter with a built-in 11-pin connector. The first generation Samsung MHL 2.0 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 second generation 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 Type-C specification allows MHL enabled source and display devices to be connected through the 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, and depending on video resolution: USB 3.1 Gen 1 or 2) and power charging (up to 100W via USB Power Delivery), 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, i.e., when connecting to superMHL, USB Type-C, and MHL-enabled HDMI, otherwise, an active cable adapter/dongle 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 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.

In common MHL Alt Mode implementations on mobile/tablet/laptops, the video from the GPU will be converted to MHL signal by using a MHL transmitter chip. The transmitter chips often accept video in MIPI (DSI/DPI) or HDMI format and covert 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 covert the MHL signal to HDMI signal format.

superMHL (32-pin)

On January 6, 2015, MHL introduced the new reversible superMHL connector. This 32 pin connector can carry concurrent video, data and power charging all in a slim, consumer-friendly form factor. A reversible design means that consumers don't have to worry about the plug's orientation or the cable's direction.

Comparison with SlimPort / Mobility DisplayPort (MyDP)

SlimPort is a proprietary alternative to MHL, based on the DisplayPort 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. Implementers of SlimPort may be subject to the MPEG-LA patent pool license for DisplayPort. On March 5, 2015, the MPEG LA announced their DisplayPort license, which is US$0.20 per DisplayPort product.

Announcements and products

MHL announced on January 6, 2015 the superMHL, the first audio/video specification with support up to 8K and a new consumer-friendly, reversible superMHL connector for CE devices

MHL announced on November 17, 2014 MHL Alternate Mode ("Alt Mode") for the USB Type-C specification

MHL announced on August 20, 2013 the MHL 3.0 specification with major advancements for mobile and CE connectivity

MHL announced on August 26, 2013 its MHL Experience Program with SEGA, PowerA, Nyko, MobiSystems, Green Throttle and FilmOn.TV

MHL announced on May 28, 2013 that it had reached 200 adopter milestone

Samsung March 14, 2013, Samsung release Galaxy S4 with MHL 2.0

HTC February 19, 2013, HTC release the New HTC One with MHL

MHL announced on January 7, 2013 that there was an installed base of more than 220 million products and greater than 200 products in the marketplace.

Hyundai announced on January 4, 2013 that it would be showing working versions of future vehicle infotainment systems, including MHL technology.

Silicon Image expanded its MHL product line with four new products that included the latest MHL 2.0 features on September 25, 2012.

LG Electronics available on December 4, 2011 AT&T Wireless and LG Electronics Nitro HD (AT&T) / Optimus LTE (LTE carriers), a True HD AH-IPS panel display on the device with MHL output abilities for any TV equipped with HDMI input.

HTC announced at the 2011 CTIA that their "EVO 3D" mobile device supports MHL output and in addition that the HTC "Sensation" will also have this capability, as well as its successor, the "Sensation XE". The HTC Rezound, which is a sister device to the Sensation XE also has the MHL port.

Samsung announced at the 2011 Mobile World Congress that their Galaxy S II mobile devices feature MHL connections.

Onkyo and Silicon Image announced on December 21, 2011 the world's first A/V receivers featuring InstaPrevue and MHL technologies.