TMS320F28027: Operating C2000 with unequal switching frequency and sampling frequency

Hi User,

Please expect a couple of days delay for our expert to analyze and respond due to holiday on 4th Jul 2022.

Hi Nachiketa

Nachiketa Deshmukh said:

I want the sampling instant to be at the peak value (PRD value) of the 100 kHz triangular wave. 

I am unable to achieve this by making TBPRD of EPWM4 = 3000 and TBPHS of EPWM4 = 150. 

What is EPWM4 being used for? If EPWM1 is setup to be 100kHz then you can setup the ADC to trigger every time EPWM1's time base counter is equal to TBPRD (SOCASEL bit of the ETSEL register).

Best Regards,

Marlyn

Thank you, Marlyn, for your kind response. 

1. EPWM4 is not in use (corresponding GPIOs left open).

2. I want to trigger ADC on every "10th instant" when "EPWM1's time base counter is equal to TBPRD".

3. Using SOCAPRD, I can go only till the 3rd instant, but I want "10th instant". 

Nachiketa,

Nachiketa Deshmukh said:

I am unable to achieve this by making TBPRD of EPWM4 = 3000 and TBPHS of EPWM4 = 150. 

To clarify, you would like to setup EPWM4 to be the trigger for the ADC at the correct frequency? Why are you not able to achieve this? Also, why is the phase shift needed if EPWM4 is just being utilized to trigger the ADC?

Best Regards,

Marlyn

Marlyn, 

Yes, I am trying to use EPWM4 to generate SOC at the correct time instant. 

EPWM1 is at 100 kHz. EPWM4 is at 10 kHz. Both are in up-down counting mode. 

If I trigger SOC at CLOCK = Zero of EPWM4, I trigger SOC at CLOCK = Zero of EPWM 1. 

If I trigger SOC at CLOCK = PRD of EPWM4, I still trigger SOC at CLOCK = Zero of EPWM 1. 

But I want to trigger SOC at CLOCK = PRD of EPWM 1 !?

I tried to TBPHS to et the required phase shift, but since TBPRD of EPWM1 and EPWM4 are different, TBPHS is not working. 

Nachiketa,

I think for your implementation it might be easier to use a timer to trigger the ADC at the exact timing you would like:

Best Regards,

Marlyn

Marlyn, Thanks for this suggestion. 

How can I synchronize the CPU timer with the EPWM counter? Without synchronization, accurate timing is not possible. 

Hi Nachiketa, 

You could start the timer right before or after you enable the EPWM 'TBCLKSYNC' and account for the slight difference. 

Best Regards,

Marlyn

Marlyn, Thank you for your kind suggestion. Can you please point me towards a relevant resource or an example code for this synchronization? Many thanks!

Hi Nachiketa,

We do not have any examples that show this exact implementation but we do have a timer example you can reference for that part:

C:\ti\c2000\C2000Ware_version\device_support\f2802x\examples\structs\timed_led_blink 

Best Regards,

Marlyn