ADDRESS DATA
R/W
HEX 321076543210
oxxo
OXXl
1000
1001
1010
1011
1010
1101
1110
1111
FUNCTION OF REGISTER
X X XA4..
..
A0
D7..
.......
DO
D7..
.......
DO
X XD5..
..
.DO
X X X D4.
...
DO
xxxxxxxx
xxxxxxxx
P D6.
......
DO
D7..
......
DO
X X X X X D2
..
DO
W
R/W
R/W
W
R
W
W
W
W
W
6845 ADDRESS REG.
6845 DATA REG.
MODE CONTAD REG.
COLOR SELECT REG.
STATUS REGISTER
CLEAR LIGHT PEN
PRESET LIGHT PEN
REGISTER BANK ADR.
REGISTER BANK DATA
DISPLAY PAGE
I/O
REGISTER SUMMARY
The
“X”
means “don’t care” bit. Address “3D8” and “3DA” are partially expanded registers. Address “3DD”,
“3DE’, and “3DF” are new expanded registers.
3D8H (MODE CONTAD REGISTER)
BIT NAME FUNCTION
80
X
25 A/N
320
X
200 GR
B&W
EN VIDEO
HIGH RES.
BLINK
160
X
200 GR
STAND-BY
80
X
25 ALPHA-NUMERIC
COLOR GRAPHICS (320
X
200)
B&W SELECT
ENABLE VIDEO SIGNAL
HIGH RES. 640
X
200 GRAPHICS
COLOR GRAPHICS (160
X
200 OR 640
X
200)
BLINK BIT
ON
ALPHA-NUMERIC MODE
STAND-BY MODE
MODE SELECT REGISTER
Bit
0
Bit 1
Selects between
40
X
25 and 80
X
25 alpha mode, a
“1”
sets it to
80
X
25 mode.
Selects between ALPHA mode and GRAPHICS mode, a
“0”
selects ALPHA modes. In graphics mode,
the resolution is selected by combination of bit 4 and bit 6. Typically this bit “1” selects 320
X
200
Graphics mode.
Selects color or B&W mode, a “1” selects B
&
W mode, the composite-video’s color-burst and
chrominance (the CH signal) are disabled, leaving only the composite intensity levels for gray shades (the
Y
signal).
Enables the video signal at certain times when modes are being changed. The video signal should be
disabled when changing modes. The video signal should be disabled when changing modes. A “1”
enables the video signal.
Selects between high resolution 640
X
200 graphics modes and other resolution modes. When on, this bit
selects 640
X
200 graphics modes and bit 6 selects between color and B
&
W mode.
When on, this bit will change the character background intensity to the blinking attribute function for
ALPHA modes. When
off,
16 background colors are available. For normal operation, this bit should be
set to
“1”
to allow the blinking function.
Bit 2
Bit 3
Bit
4
Bit
5
F-13
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