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Position Counter and Control Unit (PCCU)
399
SPRUI07–March 2020
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Enhanced Quadrature Encoder Pulse (eQEP)
6.5.1.1 Position Counter Reset on Index Event (QEPCTL[PCRM]=00)
If the index event occurs during the 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.
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 index event reset operation.
For example, if the first reset operation occurs on the falling edge of QEPB during the forward direction,
then all the subsequent reset must be aligned with the falling edge of QEPB for the forward rotation and
on the rising edge of QEPB for the reverse rotation as shown in Figure 6-8.
The position-counter value is latched to the QPOSILAT register and direction information is recorded in
the QEPSTS[QDLF] bit on every index event marker. The position-counter error flag (QEPSTS[PCEF])
and error interrupt flag (QFLG[PCE]) are set if the latched value is not equal to 0 or QPOSMAX. The
position-counter error flag (QEPSTS[PCEF]) is updated on every index event marker and an interrupt flag
(QFLG[PCE]) will be set on error that can be cleared only through software.
The index event latch configuration QEPCTL[IEL] must be configured to '00' or '11' when pcrm=0 and the
position counter error flag/interrupt flag are generated only in index event reset mode. The position
counter value is latched into the IPOSLAT register on every index marker.
Figure 6-8. Position Counter Reset by Index Pulse for 1000 Line Encoder (QPOSMAX = 3999 or 0xF9F)
NOTE: In case of boundary condition where time period between Index Event and previous QCLK
edge is less than SYSCLK period, then QPOSCNT gets reset to zero or QPOSMAX in the
same SYSCLK cycle and does not wait for next QCLK edge to occur.
6.5.1.2 Position Counter Reset on Maximum Position (QEPCTL[PCRM]=01)
If the position counter is equal to QPOSMAX, then the position counter is reset to 0 on the next eQEP
clock for forward movement and position counter overflow flag is set. If the position counter is equal to
ZERO, then the position counter is reset to QPOSMAX on the next QEP clock for reverse movement and
position-counter underflow flag is set. Figure 6-9 shows the position-counter reset operation in this mode.
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