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Epson Research and Development
Vancouver Design Center
S1D13505 Programming Notes and Examples
X23A-G-003-07 Issue Date: 01/02/05
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
5.1.1 Registers
Figure 5-2: Memory Address Offset Registers
Registers [16h] and [17h] form an 11-bit value called the memory address offset. This
offset is the number of words from the beginning of one line of the display to the beginning
of the next line of the display.
Note that this value does not necessarily represent the number of words to be shown on the
display. The display width is set in the Horizontal Display Width register. If the offset is set
to the same as the display width then there is no virtual width.
To maintain a constant virtual width as color depth changes, the memory address offset
must also change. At 1 bpp each word contains 16 pixels, at 16 bpp each word contains one
pixel. The formula to determine the value for these registers is:
offset = pixels_per_line / pixels_per_word
REG[16h] Memory Address Offset Register 0
Memory
Address
Offset
Bit 7
Memory
Address
Offset
Bit 6
Memory
Address
Offset
Bit 5
Memory
Address
Offset
Bit 4
Memory
Address
Offset
Bit 3
Memory
Address
Offset
Bit 2
Memory
Address
Offset
Bit 1
Memory
Address
Offset
Bit 0
REG[17h] Memory Address Offset Register 1
n/a n/a n/a n/a n/a
Memory
Address
Offset
Bit 10
Memory
Address
Offset
Bit 9
Memory
Address
Offset
Bit 8
320x240
Viewport
640x480
“Virtual” Display