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Position Counter and Control Unit (PCCU)
401
SPRUI07–March 2020
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Enhanced Quadrature Encoder Pulse (eQEP)
6.5.2.1 Index Event Latch
In some applications, it may not be desirable to reset the position counter on every index event and
instead it may be required to operate the position counter in full 32-bit mode (QEPCTL[PCRM] = 01 and
QEPCTL[PCRM] = 10 modes).
In such cases, the eQEP position counter can be configured to latch on the following events and direction
information is recorded in the QEPSTS[QDLF] bit on every index event marker.
• Latch on Rising edge (QEPCTL[IEL]=01)
• Latch on Falling edge (QEPCTL[IEL]=10)
• Latch on Index Event Marker (QEPCTL[IEL]=11)
This is particularly useful as an error checking mechanism to check if the position counter accumulated
the correct number of counts between index events. As an example, the 1000-line encoder must count
4000 times when moving in the same direction between the index events.
The index event latch interrupt flag (QFLG[IEL]) is set when the position counter is latched to the
QPOSILAT register. The index event latch configuration bits (QEPCTZ[IEL]) are ignored when
QEPCTL[PCRM] = 00.
Latch on Rising Edge (QEPCTL[IEL]=01)— The position-counter value (QPOSCNT) is latched to the
QPOSILAT register on every rising edge of an index input.
Latch on Falling Edge (QEPCTL[IEL] = 10)— The position-counter value (QPOSCNT) is latched to the
QPOSILAT register on every falling edge of index input.
Latch on Index Event Marker/Software Index Marker (QEPCTL[IEL] = 11— The first index marker is
defined as the quadrature edge following the first index edge. The eQEP peripheral records the
occurrence of the first index marker (QEPSTS[FIMF]) and direction on the first index event marker
(QEPSTS[FIDF]) in the QEPSTS registers. It also remembers the quadrature edge on the first
index marker so that same relative quadrature transition is used for latching the position counter
(QEPCTL[IEL]=11).
Figure 6-10 shows the position counter latch using an index event marker.
Figure 6-10. Software Index Marker for 1000-line Encoder (QEPCTL[IEL] = 1)
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