
E–6
Window Stop (x, y) Register
These registers are used to specify the (x,y) coordinate of the lower right corner of the cross hair cursor or
auxiliary window. The Window Stop X register is made up of the Window Stop X LSB (WSPXL) and the
Window Stop X MSB (WSPXM); the Window Stop Y register is made up of the Window Stop Y LSB (WSPYL)
and the Window Stop Y MSB (WSPYM). They are not initialized and may be written to or read from by the
MPU at any time. The Window Stop is not updated until the vertical retrace interval after WSPYM has been
written to by the MPU.
WSPXL and WSPXM registers are cascaded to form a 12–bit Window Stop X register. Similarly, WSPYL
and WSPYM registers are cascaded to form a 12–bit Window Stop Y register. Bits D4–D7 of WSPXM and
WSPYM are always a logical zero.
Table J–9.
Window Stop X MSB
Cursor Position X LSB
(WSPXM)
(WSPXL)
Data bit
D7
D6
D5
D4
D3
D2
D1
D0
D7
D6
D5
D4
D3
D2
D1
D0
X Address
0
0
0
0
11
10
9
8
7
6
5
4
3
2
1
0
Index = 13h
Index = 12h
Table J–10.
Cursor Position X MSB
Cursor Position X LSB
(WSPYM)
(WSPYL)
Data bit
D7
D6
D5
D4
D3
D2
D1
D0
D7
D6
D5
D4
D3
D2
D1
D0
X Address
0
0
0
0
11
10
9
8
7
6
5
4
3
2
1
0
Index = 17h
Index = 16h
The Window Stop X value to be written is calculated as follows:
Wx = desired display screen x position
Values from 0000 (hex) to 0fff (hex) may be written into the Window Stop X register.
The Window Stop Y value to be written is calculated as follows:
Wy = desired display screen y position
Values from 0000 (hex) to 0fff (hex) may be written into the Window Stop Y register.
The values wirtten into the Window Stop X and Y registers should be relative to the first displayed pixel on
the screen; i.e. (0,0).
Note that the Window Stop location specified is the last location inside of the window. For the cross hair
cursor or auxiliary window to be displayed, the Window Start registers must specify a point on the active
display.