A method and apparatus for detecting a damaged encoder strip are described. An
encoder strip is scanned in two separate operations at two separate times, a first
operation and a second operation. The number of markings sensed in each separate
operation is counted. A circuit compares the count of markings in each separate
operation. If the count differs between the two operations, the circuit determines
that the encoder strip is damaged, and the circuit develops a signal indicating
this damage. In an embodiment, the first operation is performed during a calibration,
and the second operation is performed during a power-on, or upon operator command.
