Epson S1D13705 technical manual Advanced Techniques, Virtual Display

Epson Research and Development	Page 25
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5 Advanced Techniques

This section contains programming suggestions for the following:

•virtual display

•panning and scrolling

•split screen display

5.1Virtual Display

Virtual display refers to the situation where the image to be viewed is larger than the physical display. The difference can be in the horizontal, vertical or both dimensions. To view the image, the display is used as a window into the display buffer. At any given time only a portion of the image is visible. Panning and scrolling are used to view the full image.

The Memory Address Offset register determines the number of horizontal pixels in the virtual image. The offset register can be used to specify from 0 to 255 additional words for each scan line. At 1 bpp, 255 words span an additional 4,080 pixels. At 8 bpp, 255 words span an additional 510 pixels.

The maximum vertical size of the virtual image is the result of dividing 81920 bytes of display memory by the number of bytes on each line (i.e. at 1 bpp with a 320x240 panel set for a virtual width of 640x480 there is enough memory for 1024 lines).

Figure 5-1: “Viewport Inside a Virtual Display,” depicts a typical use of a virtual display. The display panel is 320x240 pixels, an image of 640x480 pixels can be viewed by navigating a 320x240 pixel viewport around the image using panning and scrolling.

320x240 Viewport

640x480 “Virtual” Display

Figure 5-1: Viewport Inside a Virtual Display

Programming Notes and Examples	S1D13705
Issue Date: 02/01/22	X27A-G-002-03