Radio Shack TRS-80 Model II Reference Manual page 196

Model II TRSDOS
Graphics Mode
In the Graphics Mode, the Display can be thought of as an 80 by 24 matrix, as
illustrated below:
COLUMN
0 .... 6 .... 12 ... 18 ... 24 ... 30 ... 36 ... 42 ... 48 ... 54 ... 60 ... 66 ... 72 ... 79
o
1
2
3
4
5
6
7
8
R
1~
o
~~
W
13
14
15
16
17
18
19
20
21
22
23
DISPLAY POSITIONS, GRAPHICS MODE
Note: The Display has two character sizes: 80 characters per line and 40
characters per line. The illustration above shows the 80 character per line
mode.
Each time an acceptable display character is received, it is displayed at the
current cursor position (which is set on entry to the Graphics Mode routines).
Before displaying the next character, the cursor position is advanced, as
follows:
• If the cursor is to the left of Column 79, it advances to the next column
position on the same row.
• If the cursor is at Column 79, it wraps around to Column 0 on the next
row.
Cursor motion works the same way in all directions. For example, if the
cursor is at Row 23, Column 40, and the
X'FF'
(graphics-down) code is
received, the cursor wraps around to Row 0 in the same column.
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