Table
5.
Summary
of
Available Colors
R G
B
COLOR
0
0 0
0
Black
0
0 0
1
Blue
0 0
1 0
Green
0 0
1 1
Cyan
0
1
0 0
Red
0
1 0
1
Magenta
0
1
1 0
Brown
0
1 1 1
Light
Gray
1 0 0
0
Dark
Gray
1 0 0
1
Light
Blue
1 0 1 0
Light
Green
1
0
1 1
Light
Cyan
1 1 0
0
Light
Red
1 1 0
1
Light
Magenta
1 1
1 0
Yellow
1 1 1
1
White
I
Note:
"I"
provides extra luminance (brightness) to each shade
available. Resulting in the light colors listed above, except
1"'"""""\
where the
"I"
bit
is
not recognized by some monitors.
Programming Considerations
Programming the 6845 CRT Controller
The 6845 has
19
internal registers which are used to define and control
a raster scanned
CRT
display. One
of
these registers, the Address
Register,
is
actually used as a pointer to the other
18
registers.
It
is
a
write only register which is loaded from the
CPU
by executing an
OUT
instruction to
I/O
address 3D4. The
five
least significant bits
of
the
I/O
bus are loaded into the Address Register.
In
order to load any
of
the other
18
registers, the Address Register is
first loaded with the necessary pointer and then the
CPU
may output a
value to
I/O
address 3D5 in order to load the information in the
preselected register.
The following table defines the values which must be loaded
in 6845
1"'"""""\
Registers in order to control the different modes
of
operation supported
by the attachment.
2-55
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