OFF-images

The {platform} display uses a technology called Memory LCD. From the manufacturer’s data sheet:

[The display technology] derives its name from the way the LCD pixel array is used to store image data. Each pixel in the LCD array forms a 1-bit write-only memory, with the entire display acting like a one-frame write-only buffer. This feature relieves the processor and bus from the overhead of continuous data transfers to refresh the image, as the image only needs to be written once to be retained. The image is retained indefinitely as long as there is sufficient current to do so. The LCDs also do not exhibit image retention problems, so there is no worry about keeping a single image displayed for a very long time.

This means that the display has the capability of displaying an image when the unit is off, using extremely low power (typically 50µW). The images shown when the calculator is off are called OFF-images. These bitmaps are stored on the internal USB Disk in folder \OFFIMG\. Every time the calculator is turned off, the display shows the next image in the folder and cycles back to the first image after showing the last one. To be considered valid and be displayed, images need to be the following format:

  • resolution: 400×240 px

  • depth: 1-bit

  • file format: BMP

If no OFF-image is to be found in memory, the default sleepy owl image is used.