F9D
F9E
0
F9F
3
2
1
4
3
1
2
F9D
F9E
F9F
0
F9B
F9C
F9A
F97
F98
F99
QA
QB
QCLK
QEPSTS:QDF
QPOSCNT F9C
4
5
F9F
0
QI
Index interrupt/
index event
marker
QPOSILAT
QEPSTS:QDLF
Basic Operation
1967
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
Enhanced Quadrature Encoder Pulse (eQEP) Module
34.2.2.3.1.1 Position Counter Reset on Index Event (QEPCTL[PCRM] = 00)
If the index event occurs during the forward movement, then 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
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] bits are ignored in this mode and position counter error
flag/interrupt flag are generated only in index event reset mode.
Figure 34-8. Position Counter Reset by Index Pulse for 1000 Line Encoder (QPOSMAX = 3999 or F9Fh)