Repair manual

2-52
THEORY OF OPERATION
Upon command, the octal addressable latch outputs the necessary
drive pulses to the stepper motor drive network. The stepper
motor drive network properly phases the output pulses from the
octal addressable latch and then applies them via connector J6 to
the stepper motor. The stepper motor rotates the filter wheel
assembly in a clockwise (CW) direction with respect to the front
of the Digital Palette.
When the double notch in the filter wheel assembly passes the
photo interrupter (position sensor), two filter wheel sense
(FWSENSE) pulses are applied via connector J8 to a dual 4-line
to 1-line data selector/multiplexer network. Upon command, this
network converts the two FWSENSE pulses generated by the
photo interrupter into a 2-bit filter wheel sense signal. It applies
this 2-bit filter wheel sense signal onto the Address/Data
communications bus.
Specified data select signals from the microprocessor network
inputs the 2-bit filter wheel sense signal via the Address/Data
communications bus to the microprocessor network indicating that
the filter wheel assembly reached its start (no filter) position. The
microprocessor network decodes these filter wheel sense pulses.
If it is determined that the filter wheel is in its start (no filter)
position, the microprocessor network stops sending filter wheel
position output data to the stepper motor drive network. The
stepper motor stops, leaving the filter wheel in its start position.
Subsequent Expose Color commands decoded by the
microprocessor network cause the stepper motor to rotate the filter
wheel to the specified colored filter position prior to its exposure
sequence.
2) Exposure Operation
When the Digital Palette creates a colored print or slide of a
computer-generated image, sequential colored exposures take
place. The red components of the image are exposed first, and
then the green and the blue components.
Before an exposure takes place, the Expose Color command
decoded by the microprocessor network causes the applicable
colored filter (red, green, or blue) to be placed between the
displayed image items with that color and the selected camera.
This command is sent by the host computer via the applicable
parallel interface to the Digital Palette buffer memory. Refer to