TMS320F28031:eQEP index event resets QPOSCNT at non-origin position

Tool/software:

Hello,

I am using the eQEP module on F28031, and I have a question about how QPOSCNT behaves when an index event (Z-phase) occurs.

• According to the TRM, at every index event the position-counter value is latched into QPOSILAT and QPOSCNT should be either 0 or QPOSMAX.

• If the latched value is not equal to 0 or QPOSMAX, then QEPSTS[PCEF] and QFLG[PCE] are set.

My concern is the following:

1. If an index pulse (Z) occurs at a non-origin position (for example, due to noise on the Z signal), will QPOSCNT still be reset to 0?

   • In my tests, I cannot see index events on the oscilloscope, but I suspect that noise may be triggering false Z pulses.

   • This could cause QPOSCNT to reset unexpectedly and shift the origin.

2. If this happens, how should we handle it in software?

   • Can we rely on QEPSTS[PCEF] and QFLG[PCE] to detect and ignore such invalid index events?

   • What is the recommended way to keep QPOSCNT aligned to the correct mechanical position when a false index occurs?

Additional details:

• The motor mechanical range is only 95° (it never makes a full 360° rotation).

• Current configuration:

  EQep1Regs.QEPCTL.bit.FREE_SOFT = 2;

  EQep1Regs.QEPCTL.bit.PCRM = 0; // QPOSCNT reset on index event

  EQep1Regs.QEPCTL.bit.UTE = 1; // Unit Timeout Enable

  EQep1Regs.QEPCTL.bit.QCLM = 1; // Latch on unit time out

  EQep1Regs.QPOSMAX = 0xFFFFFFFF;

  EQep1Regs.QEPCTL.bit.QPEN = 1; // QEP enable

Because the motor never reaches a full rotation, Z-phase should not normally appear in the operating range.
That’s why I suspect noise is creating false Z events that reset QPOSCNT.

 What is the recommended way to robustly avoid false origin shifts in this kind of limited-rotation application?

Thank you in advance.