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PROGRAMMING IRFORMATION
15
08
07
06
05
04
00
+·. - .•.... - - . - .. - - ••.. - - - - .• - - - -+- - -+- - ·+- - -+- - - - • - - .. - - • - . - - •. -+
"'-·
not used
I
UST
I
LPF
I
VBL
I
REGISTER ADDRESS
!
+· - - .. - - - • - .. - - .•. - - - - - - - - . - - - - -+- - -+· - -+- - -+- - - - - - ••. - - - - . - - . - ·+
ADDRESS
=
CSR BASE
+
8
Figure 2-4:
CRTC Address Register Pointer Format
Table 2·5:
CRTC Address Register Pointer Bits
+ •• - •• - •
-+ .. - .... -+-. - - ••.. - •.. - • - - - .•. - ... - . - •..•. - . - ....•.... -+
i
BITS
I
ACCESS
DESCRIPTION
+ .. - - •. - -+ .... - - .. +- - • - ... - ••• - - - - . - - ..•..••. - •.. - ..••... - - .•...
+
<15:08>
(not used)
<07>
READ
~pdate
strobe (not used)
<06>
READ
Light pen register full
(1
s
full)
<05>
READ
Vertical blank
(1
=
Vblank time)
<04:00>
WRITE
CRTc· internal register address (Table
2 - 6)
+· - ••... ·+· - .• - . - -+· ...•....•.......•...•.. - - •..•• - .. - . - ..• - ..• ·+
Table 2-6:
CRTC Internal Registers
+·. ·+· .. - - . . . . . . . . . . . - ...... ·+·. - .. - . . . . . . . . . . - . . . . . . . . . - . - .. - .
·+
•REG· NAME
l
DESCRIPTION
+·. ·+· - - . - . - . - ..... - ........ ·+· .......... - ...... - . - . - - ....... - - ·+
00
Horizontal Total
The
total
number
of
character
times in a line, minus 1.
01
Horizontal Displayed
The
total
number
of
displayed
02
Hsync Positon
03
Hsync/Vsync Widths
04
Vertical Total
05
Vertical Total Adjust
06
Vertical Displayed
07
Vsync Position
characters in a line.
Defines the
number
of
character
times
until
Hsync
{horizontal
sync) .
.
Four bits each are used to
define
the
Hsync
pulse
width
and
the
Vsync (vertical sync) pulse width.
Total number of character rows
on
the screen, minus 1.
The
number
of
scan
lines
to
complete
tr~
screen.
The
number
of
character
rows
displayed.
Number
of
character
rows
until
Vsync.
2-5
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