Revisions Affected

B, C

Details

While using the PCRM = 0 configuration, if the direction change occurs when the index input is active, the position counter (QPOSCNT) could be reset erroneously, resulting in an unexpected change in the counter value. This could result in a change of up to ±4 counts from the expected value of the position counter and lead to unexpected subsequent setting of the error flags.

While using the PCRM = 0 configuration [that is, 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. 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.

If the direction change occurs while the index pulse is active, the module would still continue to look for the relative quadrature transition for performing the position counter reset. This results in an unexpected change in the position counter value.

The next index event without a simultaneous direction change will reset the counter properly and work as expected.

Workarounds

Do not use the PCRM = 0 configuration if the direction change could occur while the index is active and the resultant change of the position counter value could affect the application.

Other options for performing position counter reset, if appropriate for the application [such as Index Event Initialization (IEI)], do not have this issue.