The Display Serial Interface (DSI) is a specification by the

Mobile Industry Processor Interface MIPI Alliance is a global business alliance that develops technical specifications for the mobile ecosystem, particularly smart phones but including mobile-influenced industries. MIPI was founded in 2003 by ARM, Intel, Nokia, Samsung, STMicroele ...

(MIPI) Alliance aimed at reducing the cost of

display controller A video display controller or VDC (also called a display engine or display interface) is an integrated circuit which is the main component in a video-signal generator, a device responsible for the production of a TV video signal in a computing ...

s in a

mobile device A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical ...

. It is commonly targeted at LCD and similar display technologies. It defines a

serial bus In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are ...

and a communication protocol between the host, the source of the image data, and the device which is the destination. The interface is closed source, which means that the specification of the interface is not open to the public. The maintenance of the interface is the responsibility of the MIPI Alliance. Only legal entities (e.g. companies) can be members. These members or the persons commissioned and approved by them have access to the specification in order to use it in their possible applications.

History

Design

At the

physical layer In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer; The layer most closely associated with the physical connection between devices. This layer may be implemented by a PHY chip. The ...

, DSI specifies a high-speed (e.g. 4.5Gbit/s/lane for D-PHY 2.0)

differential signaling Differential signalling is a method for electrically transmitting information using two complementary signals. The technique sends the same electrical signal as a differential pair of signals, each in its own conductor. The pair of conducto ...

point-to-point serial bus. This bus includes one high speed clock lane and one or more data lanes. Each lane is carried on two wires (due to differential signaling). All lanes travel from the DSI host to the DSI device, except for the first data lane (lane 0), which is capable of a bus turnaround (BTA) operation that allows it to reverse transmission direction. When more than one lane is used, they are used in parallel to transmit data, with each sequential bit in the stream traveling on the next lane. That is, if 4 lanes are being used, 4 bits are transmitted simultaneously, one on each lane. The link operates in either low power (LP) mode or high speed (HS) mode. In low power mode, the high speed clock is disabled and signal clocking information is embedded in the data. In this mode, the data rate is insufficient to drive a display, but is usable for sending configuration information and commands. High speed mode enables the high speed clock (at frequencies from tens of megahertz to over one gigahertz) that acts as the bit clock for the data lanes. Clock speeds vary by the requirements of the display. High speed mode is still designed to reduce power usage due to its low voltage signaling and parallel transfer ability. The communication protocol describes two sets of instructions. The Display Command Set (DCS) is a set of common commands for controlling the display device, and their format is specified by the DSI standard. It defines registers that can be addressed and what their operation is. It includes basic commands such as sleep, enable, and invert display. The Manufacturer Command Set (MCS) is a device-specific command space whose definition is up to the device manufacturer. It often includes commands required to program

non-volatile memory Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Non-volatile memory typic ...

, set specific device registers (such as

gamma correction Gamma correction or gamma is a nonlinear operation used to encode and decode luminance or tristimulus values in video or still image systems. Gamma correction is, in the simplest cases, defined by the following power-law expression: : V_\text = ...

), or perform other actions not described in the DSI standard. The packet format of both sets is specified by the DSI standard. There are Short and Long Packets, Short Packet is 4 bytes long; Long Packet can be of any length up to 2¹⁶ bytes. Packets are composed of a DataID, Word count,

Error Correction Code In computing, telecommunication, information theory, and coding theory, an error correction code, sometimes error correcting code, (ECC) is used for controlling errors in data over unreliable or noisy communication channels. The central idea is ...

(ECC), Payload and

Checksum A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data ...

(CRC). Commands that require reading data back from the device trigger a BTA event, which allows the device to reply with the requested data. A device cannot initiate a transfer; it can only reply to host requests. Image data on the bus is interleaved with signals for horizontal and

vertical blanking interval In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field and the beginning of the first visible line of the next fram ...

s (porches). The data is drawn to the display in real time and not stored by the device. This allows the manufacture of simpler display devices without frame buffer memory. However, it also means that the device must be continuously refreshed (at a rate such as 30 or 60 frames per second) or it will lose the image. Image data is only sent in HS mode. When in HS mode, commands are transmitted during the vertical blanking interval.

Applicances

It can be used to control displays and touch controls for example.

References

{{Reflist
Display Interface Specifications
- MIPI Alliance
Example 5" Display from Waveshare (also have a look at other vendors like CUQI or Elecrow etc. pp.) to show up the applicance of Display and touch control
MIPI Alliance standards Serial buses

History

Design

Applicances

See also

References