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Display & Interfaces

In addition to parameters such as size, resolution, or brightness, when choosing a display developers must also consider the control interface.
The display interface is an important component, since it is responsible for transferring the image to be displayed from the computer to the screen as efficiently as possible. On the one hand, the choice will depend on the interfaces offered by the panel manufacturers and, on the other, one must also take into account the parameters of the controlling CPU. The following is an overview of what I refer to as the "internal interfaces" and for which type of displays the respective interfaces normally are used. I²C (Inter-Integrated Circuit, or I2C) This interface is used in small displays with low resolution, since the data speed required for the transmission of image information does not need to be so high. Naturally, these are small TFTs with up to 320x240 pixels, graphic LCDs, or PMOLED displays. Advantages:
  • low energy consumption
  • insensitive to interference
  • simple application and troubleshooting
  • bandwidth up to 1Mbit/sec
SPI (Serial Peripheral Interface) SPI is also used in small displays with low resolution. In order to fit higher resolution displays with SPI, one must provide for additional intelligence (memory, controller) on the panel side, since the interface speed does not suffice for direct image transmission. The data must be buffered in the display before they can be displayed. Advantages:
  • Simple implementation
  • Longer lines possible
  • Faster than I²C
  • Bandwidth up to approx. 10Mbit/sec
MCU (Microcontroller Unit) This is a simple parallel interface where an 8(9)-bit or 16(18)-bit wide data bus connects all peripheral units in a microprocessor system with the CPU. Based on the two original µC technologies, the interfaces can be operated both in 8080 and 6800 compatible modes. Due to the parallel data processing and the resulting higher bandwidth, it is possible to control medium-size displays and a medium colour depth. Advantages:
  • Easy integration in the system
  • Also suitable for medium-size displays
  • Bandwidth up to approx. 120Mbit/sec
RGB (red, green, blue) The RGB interface is an exceptional case of a parallel interface where no video memory is required on the display side. RGB is widely used in small and medium-size displays. Advantages:
  • Relatively low costs as a result of its mature technology
  • High performance
  • Bandwidth up to 1.2Gbit/s
LVDS (Low-Voltage Differential Signalling) LVDS is currently the most widely used interface standard for displays. The LVDS interface is used in medium-sized and large displays. Advantages:
  • Low power consumption
  • Very good EMC behaviour
  • Small number of lines
  • Bandwidth up to 3.125Gbit/s
eDP (embedded Display Port) eDP is a standard which was defined by VESA (Video Electronics Standards Association) in 2008. This type of interface is usually encountered in large monitor panels. Advantages:
  • Scalable
  • Easy integration
  • Low system costs
  • Bandwidth of 1.62Gbits/s per lane
MIPI DSI (Mobile Industry Processor Interface – Display Serial Interface) Currently, only a small number of displays using MIPI DSI are available for industrial applications. The displays offered are mostly those originating from mobile telephone or tablet applications, i.e. medium-size (5", 10.1") displays with high resolution. It is becoming evident, however, that this range will gradually increase in the future. Manufacturers like Qualcomm have embedded the interface in their chipsets and believe that there is also a market for this interface among industrial customers. Moreover, the MIPI consortium is encouraging its adoption in other areas as well, for instance in automotive or digital signage applications. Advantages:
  • Low energy consumption
  • High data throughput
  • Little electromagnetic interference
  • Small number of pins
  • Bandwidth up to 6/12Gbit/s
Vx1 (V-by-One) In 2007, Thine Electronics, too, developed an interface intended to replace LVDS in large displays. The advantage of Vx1 is that despite having a similar structure to LVDS, it is also possible to use affordable twisted-pair copper cables (merely the impedance of 100Ω must be met), and the achievable transmission speed is nevertheless higher. Despite the advantage of low-cost hardware, this interface has so far failed to make a breakthrough. Advantages:
  • It is possible to use standard cables
  • No software adjustment
  • Bandwidth up to 4 Gbit/s
Therefore, when choosing a suitable display, optics is not the end of the story; selecting the right interface requires an equal amount of attention. We will support you in your considerations. Did you find the above interesting? A more detailed article is available for download here (.docx file). About CODICO CODICO stands for design-in-distribution of high-quality electronic components. Its wide range of products includes active and passive components and interconnect systems. The company operates from its Austrian headquarters in Perchtoldsdorf, south of Vienna as an independent, privately-owned enterprise and maintains several sales offices in Germany, Denmark, Italy, France, the Czech Republic, Slovenia, and the UK, also cooperating with partner companies in Central and Eastern Europe. Backed by a high level of technical expertise, CODICO places a key focus on design-in services. CODICO's distinguishing feature consists in the technical support it provides from the development phase to the final product, and its commitment to selling exclusively high-quality products. www.codico.com
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2019-10-11 15:09 V14.5.0-2