Enhanced Quadrature Encoder Pulse (eQEP) Module
15.4.2.4.1.3 Position Counter Reset on the First Index Event (QEPCTL[PCRM] = 10)
If the index event occurs during forward movement, then the position counter is reset to 0 on the next
eQEP clock. If the index event occurs during the reverse movement, then the position counter is reset to
the value in the QPOSMAX register on the next eQEP clock. Note that this is done only on the first
occurrence and subsequently the position counter value is not reset on an index event; rather, it is reset
based on maximum position as described in
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 QEPSTS registers. It also remembers the quadrature edge on the first index
marker so that same relative quadrature transition is used for software index marker (QEPCTL[IEL]=11).
15.4.2.4.1.4 Position Counter Reset on Unit Time out Event (QEPCTL[PCRM] = 11)
In this mode, the QPOSCNT value is latched to the QPOSLAT register and then the QPOSCNT is reset
(to 0 or QPOSMAX, depending on the direction mode selected by QDECCTL[QSRC] bits on a unit time
event). This is useful for frequency measurement.
15.4.2.4.2 Position Counter Latch
The eQEP index and strobe input can be configured to latch the position counter (QPOSCNT) into
QPOSILAT and QPOSSLAT, respectively, on occurrence of a definite event on these pins.
15.4.2.4.2.1 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).
shows the position counter latch using an index event marker.
1661
SPRUH73H – October 2011 – Revised April 2013
Pulse-Width Modulation Subsystem (PWMSS)
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