sed1355 ETC-unknow, sed1355 Datasheet - Page 179

• Manufacturer Part Number: sed1355
• Description: Sed1355 Embedded Ramdac Lcd/crt Controller
• Manufacturer: ETC-unknow

Epson Research and Development
Vancouver Design Center
5 Advanced Techniques
5.1 Virtual Display
Programming Notes and Examples
Issue Date: 99/04/27
This section presents information on the following:
• virtual display
• panning and scrolling
• split screen 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
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.
Seldom are the maximum sizes used. Figure 5-1: “Viewport Inside a Virtual Display,” depicts a
more 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.
Figure 5-1: Viewport Inside a Virtual Display
320x240
Viewport
“Virtual” Display
640x480
11
or 2048 words. In 1 bpp display
X23A-G-003-05
SED1355
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