Book Analog Interfacing to Embedded Microprocessors
the motor continuously rotates, the registers will eventually overflow. The
Figure 7.32
LM628/LM629 index timing.
194 Analog Interfacing to Embedded Microprocessors
software must take this condition into account. This is especially true if the
software uses, say, 64-bit math. It would be possible, in software, to add an
offset to a current position and get an answer that is greater than 32 bits:
for example, C017B390 (hex) plus 40000000 (hex) results in a result larger
than 32 bits and cannot be stored in the LM628/9 registers.
• When using the index input, the LM629 will capture the count. This
becomes, in effect, the “zero” or “home” position of the motor, and all
moves are relative to that position. However, the 32-bit position counter is
not reset by the index. So the software must offset moves from the index
position.
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