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USB Incremental Encoder Interface Hardware
Deva037 USB Encoder Interface User’s Manual
To use the marker input the marker circuit must be enabled. Once a positive edge has
occurred on the marker input the counter is latched when both A and B are at logic one. The
marker latch register may now be read while the counter continues to maintain position. To
enable the marker latch to capture a further event the marker function should be disabled and
then re-enabled. Marker synchronisation with signals A and B can optionally be disabled.
4.2.3
Zero input
The Z input circuit, designated zero, is a positive edge triggered input which can
asynchronously latch the counter value. It has been provided to maintain compatibility with
previous issues and offer more flexibility when connecting encoders. The marker function,
which accurately latches the counter value, is equally suited to performing a zero-type
operation by using the latched value as an offset which is subsequently subtracted from the
counter reading.
4.2.4
Touch Probe Interface
The Deva037 incorporates a touch probe input. This input provides the correct signal
conditioning to allow a volt-free contact type touch probe to be used. The probe function
works like the marker function but latches all three axis counters simultaneously. Unlike the
marker function it operates asynchronously and hence does not require that the A and B
signals be at a logic one level. The probe function has its own enable bit.
The device also incorporates an output to drive the probe LED, an output to drive an audible
sounder, and a further input to allow the probe to be controlled via a footswitch.
4.2.5
Optical Edge Detector Input
The Deva037 incorporates a dual input optical edge detector system. Encoder positions can
be latched when the optical level present at the signal input crosses a pre-programmed
threshold. Furthermore, the reference input can be used improve the signal quality by
receiving light from the illumination source and cancelling out any disturbances present in the
light signal.