Commodore 128 Programmer's Reference Manual page 335

PROGRAMMING THE 80-COLUMN (8563) CHIP 325
' R4 VERTICAL TOTAL
The number of character rows, minus 1, between successive vertical sync pulses. This
f number includes the displayed rows, vertical border and the blanking interval during the
' vertical sync pulse and determines the vertical sync rate.
H R5(4-0) VERTICAL TOTAL ADJUST
r | The number of scan lines added to the end of the frame for fine adjustment of the
vertical sync rate. In the interlaced sync and video mode, this register should be
0 programmed with a value equal to twice the number of scan lines desired.
! I
R6 VERTICAL DISPLAYED
The number of character rows displayed in a frame. This number sets the height of the
p displayed part of the frame.
R7 VERTICAL SYNC POSITION
r-) The number of character rows, plus 1, from the first displayed character row to the
1 j start of the vertical sync pulse. This number should be greater than the number in R6
(vertical displayed).
P R8(l-0) INTERLACE MODE CONTROL
' There are three raster-scan display modes: non-interlaced, interlaced sync, and interlaced
sync and video. The non-interlaced mode has been described above. In this mode, each
P scan line is refreshed at the vertical sync rate. This mode is selected by setting R8(l-0)
i 1 equal to 00 or 10.
In the interlaced sync mode [R8(l-0) = 01], even and odd fields alternate to
,_, generate frames. The same information is displayed in both odd and even fields but the
I vertical sync timing causes the scan lines in the odd fields to be displaced from those in
r the even fields by one-half scan line. The spaces between adjacent scan lines are filled,
resulting in a higher-quality character on monitors designed to receive interlaced video.
f"l In the interlaced sync and video mode [R8(l-0) = 11] even and odd fields
< ■ \ alternate to generate frames. Odd fields display odd scan lines, and even fields display
even scan lines. This doubles the vertical character density on the screen. To display
p twice as many character rows, the user must re-initialize the 8563 registers. In this
j | mode, the vertical sync width [R3(7^4)] and the vertical total adjust [R5(4-O)] should be
programmed with even values. The duration of each of these events (in scan lines) will
be one half the value programmed into the registers.
' ' R9(4-0) CHARACTER TOTAL, VERTICAL
The number of scan lines, minus 1, in a character. This number includes the displayed
H part of a character and the vertical intercharacter spacing below the displayed part. This
! register sets the vertical dimension of a character and the vertical dimension of a
character row.