Instruction manual

Updating the Bt459 Color Map
To write the color map, load the Bt459’s address register low byte with the desired
color map entry address (0000...00FF). Write the red, green, and blue values in
three successive RAMDAC write operations to the color map.
After the blue value is written, the Bt459 automatically increments the address
register low byte to the next color map location. The same sequence may be
repeated 256 times to update the color map fully.
Updating the Bt459 Control Registers
To access the Bt459 control registers, load the address register low byte and
address register high byte with the desired control register address, then perform
the read/write I/O operation.
On-Chip Cursor Operation
The Bt459 has an on-chip, three color, 64x64 pixel user-definable cursor. The
cursor pattern is provided by the cursor RAM, which is accessed by the main
processor through the TURBOchannel. The cursor (x,y) register positions the
cursor. For more information about the Bt459 cursor operation, refer to the Bt459
RAMDAC Specification.
CXTurbo Graphics Subsystem: 300/500 Models 6–23