SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
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 (EQEP_QDEC_QEP_CTL[29-28] PCRM = 0b01 and EQEP_QDEC_QEP_CTL[29-28] PCRM = 0b10 modes).
In such cases, the EQEP position counter can be configured to latch on the following events and direction information is recorded in the EQEP_QEP_STS_CT[4] QDLF bit on every index event marker.
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 (EQEP_QINT_EN_FLG[26] IELI_FLG) is set when the position counter is latched to the EQEP_QPOSILAT register. The index event latch configuration bits are ignored when EQEP_QDEC_QEP_CTL[29-28] PCRM = 0b00.
When Position counter reset on an index event mode is selected through EQEP_QDEC_QEP_CTL[29-28] PCRM bit field (value: 0h), EQEP_QDEC_QEP_CTL[21-20] IEL bit field must be configured to 0h and position counter value is latched into the EQEP_QPOSILAT[31-0] QPOSILAT register for every index marker.
The position counter value (QPOSCNT) is latched to the EQEP_QPOSILAT register on every rising edge of an index input.
The position counter value (QPOSCNT) is latched to the EQEP_QPOSILAT register on every falling edge of index input.
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 (EQEP_QEP_STS_CT[1] FIMF) and direction on the first index event marker (EQEP_QEP_STS_CT[6] FIDF) in the EQEP_QEP_STS_CT 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 (EQEP_QDEC_QEP_CTL[21-20] IEL = 0b11).
Figure 12-2698 shows the position counter latch using an index event marker.