Repair manual

2-53
THEORY OF OPERATION
paragraph 4 in this Section of the Service Manual for a functional
description of the Digital Palette buffer memory.
Upon receipt of this command, the microprocessor network
removes and executes the Expose Color command from the buffer
memory. It flags the specified colored filter instructions from the
EPROM. The image data specified by this command will be
exposed once the the filter wheel is rotated to the specified colored
filter position.
The EPROM applies the specified colored filter instructions to the
input of the microprocessor network via the Address/Data
communications bus. The microprocessor network decodes these
colored filter instructions from the EPROM and then applies the
colored filter output data via the Address/Data communications
bus to the octal addressable latch in the stepper motor drive
network.
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.
As the stepper motor rotates the specified colored filter into its
exposure position, a notch in the filter wheel adjacent to the
selected colored filter interrupts the photo interrupter
(position sensor). Interrupting this sensor generates a filter wheel
sense (FWSENSE) pulse/pulses that is applied via connector J8 to
a dual 4-line to 1-line data selector/multiplexer network.
Upon command, this network converts the FWSENSE pulse
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 reached its selected colored filter position. The
microprocessor network determines when the specified colored
filter is properly positioned by decoding the 2-bit filter wheel
sense signal.