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Epson Research and Development
Page 29
Vancouver Design Center
Programming Notes and Examples S1D13505
Issue Date: 01/02/05 X23A-G-003-07
5 Advanced Techniques
This section presents information on the following:
• virtual display
• panning and scrolling
• split screen display
5.1 Virtual Display
Virtual display refers to the situation where the image to be viewed is larger than the
physical display. This can be in the horizontal, the vertical or both dimensions. To view the
image, the display is used as a window (or viewport) 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 registers are used to determine the number of horizontal pixels
in the virtual image. The offset registers can be set for a maximum of 2
11
or 2048 words.
In 1 bpp display modes these 2048 words cover 16,384 pixels. At 16 bpp 2048 words cover
1024 pixels.
The maximum vertical size of the virtual image is the result of a number of variables. In its
simplest, the number of lines is the total display buffer divided by the number of bytes per
horizontal line. The number of bytes per line is the number of words in the offset register
multiplied by two. At maximum horizontal size, the greatest number of lines that can be
displayed is 1024. Reducing the horizontal size makes memory available to increase the
virtual vertical size.
In addition to the calculated limit the virtual vertical size is limited by the size and location
of the half frame buffer and the ink/cursor if present.