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I am doing some reading about interfacing displays with an MCU. I came across this block diagram:

display block diagram

About the display controller, the following is mentioned:

The display controller is continuously “refreshing” the display, transferring the framebuffer content to the display glass 60 times per second (60 Hz). The display controller can be embedded either in the display module or in the MCU.

Today, we have a lot of use cases where display is static for most of the time. Foe example - our laptop and mobile screens.

Does the controller refresh the screen while displaying a static image? Or does it dynamically starts refreshing when there is a change? (E-ink displays are static when no change is required, for example.)

If the controller refreshes the display even during a static screen, is it not a rather inefficient way to do it? Are they doing it to give a better experience to the user (making the display more snappy)?

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  • \$\begingroup\$ It depends. Computer screens/TVs are constantly refreshing. Other devices may vary \$\endgroup\$
    – Eugene Sh.
    May 21, 2021 at 17:20
  • \$\begingroup\$ Note, that the reason for constant refresh is partially historical, when the screens were CRT and the constant refresh was a must and was "built-in" into the common display input signal standards (such as VGA) \$\endgroup\$
    – Eugene Sh.
    May 21, 2021 at 17:33

1 Answer 1

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As you say, E-ink displays are inherently static. Most other display technologies are not inherently static1, and must be refreshed in order to prevent the pixels states from being lost.

In LCDs, the pixel intensity is determined by the charge on a thin-film transistor embedded in the display panel. This charge leaks away over time. Also, LCDs must be driven with an AC signal (the polarity of the charge must be reversed periodically), which requires refresh logic.

In OLEDs, the pixel intensity is determined by the current through the OLED. Since it isn't possible to run millions of different currents simultaneously, the display is multiplexed, which again requires refresh in order to create the illusion of a static display.


1 There used to be a technology called "AC plasma display" that is inherently static, but nobody uses that any more. Mechanical flip-dot displays are also static, but they are slow and very low resolution.

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  • \$\begingroup\$ Charge leak and multiplexing explains it. Thanks Dave, for taking out your time to answer this. :) \$\endgroup\$ May 21, 2021 at 18:29

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