Book Analog Interfacing to Embedded Microprocessors
One caution if you use this technique: the LM628/9 responds to the
index input when both the encoder channels are low, so the sensor output
has to be low while both encoder channels are low. To avoid multiple
index capture events from a single sensor input signal, be sure the index input
to the LM628/9 occurs for only one encoder cycle, regardless of how long
the actual sensor input lasts. In the actual application, a small CPLD handled
the index inputs for multiple LM629s. Figure 7.32 shows how the timing
worked.
The interrupt output can be asserted for any combination of various con-
ditions, including a breakpoint, index pulse, wraparound, position error, or
command error. Which conditions generate an interrupt are controlled by
the software, by setting a mask byte in the LM628/9. The interrupt output is
level sensitive and true when high.
When using the LM628/9 motor controller, there are some software
considerations:
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