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2.1.4. Display registers
The display registers are used to control display position on the screen.
MSB
R#18
Register #18 controls horizontal and vertical alignment on the screen. Please refer to
the table below.
7
H
Left
V
Top
MSB
R#23
This register R#23 sets the value of the first line to display on the screen. Virtual
screen size is 256 lines, visible vertical screen size can be 192 or 212 depending on LN bit
of register R#9. Setting R#23 to value other than 0 may display un-initialized parts of the
memory which may look as garbage. Display of virtual screen is performed in cycle,
meaning that when increasing value of R#23 top of virtual screen appears at the bottom of
visible screen. Please see pictures below.
Original screen* in
GRAPHIC1 mode
* "Auf Wiedersehen Monty" image, a property of Gremlin Graphics. Used in this book for educational purposes only
© 1985 ASCII CORP. / NIPPON GAKKI CO.
7
6
5
V3
V2
V1
...
1
...
...
...
...
7
6
5
DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0
Offset screen*, horizontal
scan line is 256 dots,
GRAPHIC1 mode, top
appears at the bottom
4
3
2
V0
H3
H2
Value
0
Center
Center
4
3
2
Page 20 of 108
1
0
LSB
H1
H0
Display adjust
register
15
...
...
...
...
..
1
0
LSB
Vertical offset
register
TEXT1 mode, horizontal
scan line is 240 dots,
garbage in un-initialized
memory space
© 2010-2015 Eugeny Brychkov
8
Right
Bottom
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