Best way to do Duty cycle measurement

Manu36

Other Parts Discussed in Thread: TMS320F28027F, TMS320F28027

Hi,

I use TMS320F28027F and I need to measure the duty cycle on a PWM input.

The example 4 in capture module reference guide is a way to do it :

But with this solution, perhaps I could have problems with EMC glitches (even if i have an HW filter), and also resolution problem because i try to be independent of the PWM frequency.

Competitors products have a gated timer mode, that is to say the timer is incremented only if the input pin is 1. So I start at the same time 2 timers, one is free the other is gated. When the free one reach the maximum value, an interrupt is generated and I only have to do a simple divide between the 2 timers register and i have an accurate result, without thinking about glitches.

Is there a way to do the same with TMS320F28027?

Regards.

Emmanuel

over 11 years ago

0 Gautam Iyer over 11 years ago

Guru 192875 points

Hi Emmanuel,

Is there a way to do the same with TMS320F28027?

Did you try using the eCAP module for this purpose? 6253.eCAP.pdf

Regards,

Gautam

0 Manu36 over 11 years ago in reply to Gautam Iyer

Expert 1350 points

Gautam Iyer said:
Did you try using the eCAP module for this purpose?

Not for the moment, as I explain, if there is no other solutions, I will do as explain in example 4 of eCAP module, but I'm looking for a more robust an more insensible to PWM frequency (and I think gated timer is more accurate than eCAP for this).

Regards.

Emmanuel

0 Gautam Iyer over 11 years ago in reply to Manu36

Guru 192875 points

(and I think gated timer is more accurate than eCAP for this).

If you feel so then where's the hesitation? As for gated timer mode, as per my knowledge there isn't any mode in F28027.

Regards,

Gautam

0 Manu36 over 11 years ago in reply to Gautam Iyer

Expert 1350 points

Gautam Iyer said:
If you feel so then where's the hesitation?

I'm a new user of TI Microcontrollers, so even if I have take a look on datasheet, perhaps I have miss a special module for that or another part.

Another difficult with eCAP will be 100% and 0% duty cycle measure (I will try testing the overflow status).

Regards.

Emmanuel.

0 Gautam Iyer over 11 years ago in reply to Manu36

Guru 192875 points

I'm a new user of TI Microcontrollers, so even if I have take a look on datasheet, perhaps I have miss a special module for that or another part.

Yes, to get a complete idea about the device I would suggest you to go through these peripheral docs:

http://www.ti.com/product/TMS320F28027/technicaldocuments#doctype6

Regards,

Gautam

0 Manu36 over 11 years ago in reply to Gautam Iyer

Expert 1350 points

eCAP works correctly but is there a way to read the logical state of the eCAP input pin without changing the GPIO configuration?

I need this if duty cycle is 0% or 100%.

Regards.

Emmanuel

0 Manu36 over 11 years ago in reply to Manu36

Expert 1350 points

OK it seem just reading the GPIO works, even if ecap mode is enabled, there xas a bug in my code.

Regards

0 Gautam Iyer over 11 years ago in reply to Manu36

Guru 192875 points

So, you're able to implement your logic using eCAP?

0 Manu36 over 11 years ago in reply to Gautam Iyer

Expert 1350 points

Gautam Iyer said:
So, you're able to implement your logic using eCAP?

Yes, it works fine "on the table". Using and set up is quite simple (starting from the control suite example).

Today I will try to simulate EMC glitch and I will also try with very large and very small duty cycle.

Regards.

Emmanuel

0 Gautam Iyer over 11 years ago in reply to Manu36

Guru 192875 points

Yes, it works fine "on the table". Using and set up is quite simple (starting from the control suite example).

That's great, Emmanuel!

Today I will try to simulate EMC glitch and I will also try with very large and very small duty cycle.

Sure sure! Do share your observations.

Goodluck & Regards,

Gautam

0 Manu36 over 11 years ago in reply to Gautam Iyer

Expert 1350 points

Large and small duty cycle measuement are OK. Measure is OK down to 0.1% and up to 99.9%, lower and upper are filtered by the hardware filter and a timeout read the pin logical value to force 0% or 100%.

EMC glitch are dificults to reproduce but as small pulse are correcly detected, this must be OK.

Regards.

Emmanuel

0 Gautam Iyer over 11 years ago in reply to Manu36

Guru 192875 points

Good, Good. Thanks for the update!

Regards,

Gautam

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Best way to do Duty cycle measurement