Commodore 128 Programmer's Reference Manual page 307

PROGRAMMING THE 80-COLUMN (8563) CHIP 297
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a. Visible 8 by 8 pixel character.
b. Horizontal intercharacter spacing.
c. Vertical intercharacter spacing.
Figure 10-3.
The horizontal unit of measure within a character is a pixel. The vertical unit of
measure within a character is called a scan line. A scan line is a single horizontal row of
scanned pixels referred to as one raster. The pixel and the scan line are the smallest units
of measurement by the 8563 chip in the horizontal and the vertical directions, respec
tively. The size of the displayed character image in both pixels and scan lines is
programmable and determined by four registers within the 8563: the Character Total
(R9) (vertical), Character Total (R22) (horizontal), Character Displayed (R23) (vertical)
and Character Displayed (R22) (horizontal) Registers. These registers are described in
the register by register description at the end of this chapter.
FRAMES
A frame is a two-dimensional array (matrix) of characters, also referred to as simply the
screen. The default frame is the 80-column by 25-line screen in which characters are
displayed. Each character on the frame has a character pointer (a Display RAM byte)
that tells the 8563 which character to display in each character position within the frame.
Think of a frame as a framed picture on a wall containing a two-dimensional array
(matrix) of characters. For example, a frame specified to be 16 by 12 characters is filled
with characters as in Figure 10-4.
The frame also contains the vertical retrace and all other nonvisible portions of the
screen. The frame is programmable in size, similar to a window. The screen frame
determines the size of the viewed image, like the frame surrounding a window.
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