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Original question:

TMS320F28335: TMS320F28335 Qualification Period

TMS320F28375D: EQEP GPIO QUALIFICATION PERIOD

surendra annepu
Prodigy 50 points
Part Number: TMS320F28375D


Tool/software:

HI 

I am using eqep module to calculate  speed and postion 

first question is :1) what is min qualprd should to take at high speed (250 )[ eqep data : teeth =36,freq=255 Hz, Time = 0.006667 sec]in gpio qualification beacuse at high speed there may spikes and might there is chance that gpio cant filter or miss that spike due to high speed. if this assumption is true  what is min qualprd should be taken and sampling window for 6 samples

question : 2) if i  want to take sampling window of 0.006667 sec as mentioned in  Question 1 (on and off time of a pulse) with 6 samples i am getting Qualprd of 134000 which is not possible since qualprd is 8 bit reg so max value is 255. how to over this issue?

  • 0
    TI__Mastermind 26826 points

    Hi Surendra,

    Regarding your questions about using the eQEP module for speed and position measurement, here are my responses:

    1) The value of QUALPRD (GPIO qualification period) depends on the maximum expected frequency of the eQEP input signals (QEPA and QEPB). The GPIO's QUALPRD setting determines the sampling window for filtering noise/glitches on the input signals. A larger QUALPRD value provides a wider sampling window, which helps filter out narrow glitches but may also distort the input signal if the value is too large.

    For a speed of 250 rpm (assuming a 36-tooth encoder), the corresponding frequency would be 150 Hz (period of 6.67 ms).

    Can you confirm if you're talking about QUPRD or QUALPRD?

    Best,

    Ryan Ma

  • 0 in reply to Ryan Ma
    Prodigy 50 points

    Hii Ryan Ma

      in the above answer ----(However, for a speed of 250 rpm (assuming a 36-tooth encoder), the corresponding frequency would be 150 Hz (period of 6.67 ms). In this case, you may need a larger QUALPRD value, perhaps in the range of 200-250, to provide a wider sampling window of around 0.8-1 ms).----  for the data  i am getting the sampling window time is 0.01 m sec to  0.0125 m sec for QUALPRD ( 200 to 250) could you please cross check your calculation and reply ?

    --> if the above my calculation you came to know is right then  isn't that is 0.01 msec a less time  for qualification ? can u comment on this ? else the time is fine for sampling window ?

  • 0 in reply to surendra annepu
    Prodigy 50 points

    Hii Ryan ma

    kindly reply  for this issue

  • 0 in reply to surendra annepu
    TI__Mastermind 18411 points

    Hi Surendra,

    Please refer to this article resolving how to resolve noisy EQEP inputs. https://www.ti.com/document-viewer/lit/html/SSZT713

    Can you explain further why you need to make use of the QUALPRD as opposed to just enabling the 3/6 cycle qualification period? I think even at the higher RPM, the 6 cycle can be sufficient. Have you tested with these settings and seen incorrect readings from your encoder?

    Regards,

    Peter

  • 0 in reply to Peter Luong1
    TI__Mastermind 26826 points

    Hi Surendra,

    I have updated my initial response, let's clarify QUALPRD and QUPRD. One is done through GPIO, another is related to the eQEP module itself.

    You usually should not be needing to change QUALPRD from the GPIO as this will affect a group of GPIOs.

    Best,

    Ryan Ma

  • 0 in reply to Ryan Ma
    Prodigy 50 points

    hiii  Ryan ma 

    i am talking about qualprd in qualification.issue is  at higher rpm i am getting for  0.006667 sec sampling window duration im  getting qualprd value greater than 255 (in detail data i have posted in my starting question kindly check that )

  • 0 in reply to surendra annepu
    TI__Mastermind 26826 points

    Hi Surendra,

    Peter Luong1 said:

    Can you explain further why you need to make use of the QUALPRD as opposed to just enabling the 3/6 cycle qualification period? I think even at the higher RPM, the 6 cycle can be sufficient. Have you tested with these settings and seen incorrect readings from your encoder?

    Can you help answer this? 

    The 6 sample qualification is the max to qualify a valid input. 

    There should be no change required for the sampling frequency on these pins when using eQEP. Most people do not change the sampling frequency and only change the number of 3 or 6 samples for the input signal to be qualified to help reduce noise etc.