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Encoder Integrity Checking
V6U Revision 4 now includes broken wire detection and illegal state detection (using digital
filtering on encoder input lines). Linear Tech LTC1519 EIA-422 line receivers (with open and
short circuit guaranteed states) are used in a flip-flop structure to provide information to exist-
ing Encoder Integrity Checking (EIC) logic on the V6U.
Broken Wire & Illegal State Detection
The encoder inputs (channel A+, A-, B+, B-) are monitored by the FPGA (an on-board logic
component). The encoder inputs are sampled at 10mHz. A digital filter has been added to each
of the encoder inputs to the position counters in the FPGA. This digital filter requires that an
encoder input (channel A+, A-, B+, B-) be stable
for 4 clock cycles
(400 nanoseconds) before
a transition is recognized, i.e., encoder input states lasting less than 4 clock cycles are consid-
ered illegal and filtered out.
A broken wire condition occurs when either (A+ and A- channels) or (B+ or B- channels) are
in the same logic state for 3 consecutive sample periods (300 nsec). When a broken encoder
wire is detected, the appropriate bit (one per axis) in the broken wire status register is latched.
Use the routine
set_feedback_check(int16
axis
, int16
*state
)
to configure broken wire and il-
legal state detection. To enable feedback checking, set
state
= TRUE; to disable feedback
checking, set
state
= FALSE. After feedback checking is enabled, use the routine
get_feedback_check(int16
axis
, int16
*state
)
to read the current feedback checking configura-
tion for an axis. When feedback checking is enabled, the V6U will examine the broken wire
and illegal state registers at every DSP sample. If the DSP detects an encoder failure, an
Abort
Event
will be generated on the appropriate axis.
Use
axis_source(...)
to determine the cause of the
Exception Event.
To clear a broken encoder wire or illegal state condition, call
controller_run(...).
This function
will clear the broken wire, illegal state registers, and the
Abort Event.
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