Page
3.7
General Theory of Operation
NOTE: The scan rate of the monitor cannot refresh the display faster
than
50
Hz.
Example
for
50 Hz:
18,432/50 = 368.64 scan lines per frame
368.64/14
= 26.33
Note that the result of the above division
is
26 with a remainder of
3.
Enter
25
(one less than the number desired) into register
R4.
• Vertical Total
Adjust
Register
(R5}-
This 5-bit, write-only register
is used to lengthen the vertical total time to account for the scan lines
remaining when the value for
R4
was determined. This value
is
ex-
pressed
in
scan lines. The correct value is 6 (06H).
• Vertical Displayed Register
(R6}-
This 7-bit, write-only register de-
termines the number of character rows which will be displayed. This
value cannot exceed, but may be equal to or less than, the value
in
R4.
The default value
is
19H
(25
decimal).
• Vertical Position Register
(R7}-
This 7-bit, write-only register con-
trols the position of the vertical sync expressed
in
character rows.
This value should be less than or equal to the value of
R4.
Entering
a lower number will move the display downward, higher values move
the display upward. The default value is 19H (25 decimal).
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