How to Avoid TE Screen Clipping on Small and Medium-Sized LCD Screens

    The LCD TE pin, defined as the "Tearing Effect," primarily serves a data synchronization function, converting analog signals captured by the camera into digital image signals. The host then transmits these digital image signals to the display, which can cause image tearing. To address this issue, the TE function was introduced, allowing a complete, tear-free image frame to be transmitted to the display. Screen clipping can often occur when using a portrait screen as a landscape screen if improperly configured. If the LCD screen has a TE interface, it is recommended to connect the TE pin.

    The root cause of the TE effect is speed mismatch between the two sides. Specifically, the LCM refresh rate is faster than the host data transmission rate, and the two speeds must be within a certain range. This is achieved by ensuring that the CS cycle is between two TE cycles. That is, the CS write frequency must be no less than half the TE read frequency. The fundamental condition for tearing is overlapping read and write cycles. Typically, the write Gram rate (WR) is slower than the LCD refresh rate (TE). As long as the refresh position does not exceed the write Gram position, there will be no screen clipping. For example, if CS is slightly less than two TE cycles, and two frames of data are being refreshed, the first frame begins to be refreshed, marking the start of the GRAM read. This is relatively fast, and the data is read from older frames. The controller then begins writing to the GRAM. When it reaches about halfway through the GRAM, the frame is already refreshed. The second frame then begins to be refreshed, reading and refreshing the screen from the top of the GRAM. Only the newly written data is displayed. Before the GRAM is fully written, the read cycle will never catch up with the write cycle, and screen clipping will not occur.

    If CS is greater than two TE cycles, assuming it's equivalent to three TE cycles, then only during the third TE read cycle will the data displayed reflect the written GRAM data. The first TE reads older data, and in the second TE cycle, since the GRAM is not yet fully written, the read cycle catches up with the write cycle. This results in a display that displays both older and newer data, thus causing a TE. If TE has been successfully enabled but still experiences teering (especially noticeable during camera preview or video playback), consider the following:

1) Is the screen in portrait or landscape orientation? This causes inconsistent read and write directions for the GRAM, typically resulting in diagonal screen switching.

2) Is the clock speed too low, with the FPS less than 1/2 the LCM self-refresh rate?

3) Is the clock speed too high, exceeding the LCM self-refresh rate, causing GRAM writes to catch up with reads, leading to teering.

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