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Theory of Operation 2-13
NovaJet 500/630/700 Series Service Manual
THEORY OF
OPERATION
OUTPUT OF DETECTOR 2
COMPOSITE TRANSITION-TRIGGERED OUTPUT OF BOTH DETECTORS
OUTPUT OF DETECTOR 1
4 OUTPUT PULSES
PER OPTICAL LINE
DETECTOR 2
DETECTOR 1
ENCODER STRIP
Figure 2-9. Quadrature Signal Generation.
The direction that the Carriage Assembly is moving is known based
upon the state of one detector’s output and the direction of the transition
of the other detector’s output.
A hardware counter in the gate array increments as the Carriage
Assembly moves left and decrements as the Carriage Assembly moves
right. The hardware counter is only eight bits wide, so it cannot store a
value large enough to represent an absolute Carriage Assembly position.
Instead, it is read during the servo interrupt and its value compared
with that from the previous interrupt. This difference is used to update
the absolute position value in the software.