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TMS320F28375S: Measuring high-speed pulse periods with eQEP

Part Number: TMS320F28375S

Hi experts,

My customer wants to use the eQEP in DirectionCountMode to measure the period of an external pulse.
The cycles I want to measure are 2.929MHz (1 cycle 341.33ns) and 2.930MHz (341.1911ns).
eCAP cannot measure this frequency. (due to insufficient eCAP resolution)
Therefore, they are trying to measure the period of this frequency with eQEP's DirectionCountMode.
Example: Find the time until 500 pulses are input, and calculate the frequency from there (pulses/time = frequency).
So I have the following questions.

Q1: QUTMR (eQEP capture timer) is incremented at which timing of eQEPCLLK?
Is it the rising edge of eQEPCLK?
We set eQEPCLLK = SYSCLK = 200MHz.

Q2: Is it possible to measure these two periods? (2.929MHz (1 cycle 341.33ns) and 2.930MHz (341.1911ns)
Q3: If these cannot be measured, are there any other good solutions?

Best regards,
Sasaki

  • Hi Sasaki,

    Sorry for the inconvenience but our subject matter expert will be OOO and will return Nov. 3rd to answer your questions.

    Best regards,

    Ryan Ma 

  • Hi Sasaki-san,

    Thanks for reaching out. It sounds like you will most likely want to be making use of the edge capture unit within the eQEP peripheral (see the following app note: www.ti.com/lit/spraah1)

    Q1. The QUTMR is directly clocked off of the SYSCLK, which means that timer should be incremented on the rising edge of the SYSCLK.

    Q2. These periods you are wanting to measure should be possible with the eQEP peripheral, but we have not characterized exact maximums for this functionality so it would have to be tested. See below for the timing characteristics of the eQEP peripheral.

    Q3. The eQEP approach should be viable, but please reach out if you experience any issues with this

    Regards,

    Peter

  • Hi Peter-san,

    Thank you for your support.

    I got it.

    Best regards,
    Sasaki