TMS320F28374D: help on pwm compare registers load at a sync signal

Colombo Carlo

Part Number: TMS320F28374D

Hello everybody ,

please I need to write values in the shadow registers of compare of pwm , and ideally to be able to load at selected time or event ( like a Sync signal ).

Immediate loading is not ok for me in this case .

now looking at the TRM on page 1776 I can see 14.14.2.7 CMPCTL Register the fields : LOADASYNC & LOADBSYNC .

these seem exactly what I need but questions :

-> SYNC signal which is mentioned on page 1776 : could you confirm me which signal is this ? I m a little confused on this

--> SYNC signal impacts the PWM timing ? I need not to touch any time base , just load compare when it is needed by my SW

thank you very much

best regrads

carlo

over 7 years ago

0 Colombo Carlo over 7 years ago

TI__Mastermind 24640 points

HI everybody ,
I did some steps ,
I followed Blcok diagram as on page 1696 and using the TBCTL to sync the load : it works , no PWM timebase change , but I have from time to time glicthes --> some periods ( even if Correct compare values ) goes totally to 1 or to 0 .
please where am I wrong ?
thank you
regards
Carlo

0 Nima Eskandari over 7 years ago in reply to Colombo Carlo

TI__Guru 52040 points

Carlo,

Each ePWM has a SYNC input, which resets the ePWM timebase counter to zero (Up mode, up-down mode, when phase shifting isn't enabled which I am guessing you are not using). This sync input can come from another EPWM, Software, or other sources. In a simple case, your ePWM isn't connected to any other module, which is what i'm going to explain below.

Each ePWM can be configured to operate in different modes but the most common ones are Up mode and Up-down mode. In this case the timer TBCTR will count from 0 to period (in up-down mode 0-PRD then back down to zero). You can set up you CMPA, CMPB values to be updated from the shadow register, at CTR = 0, CTR = PRD or both CTR = PRD and ZERO. That is how the shadow registers get updated. Another note, when a software sync occurs and CTR is reset, the shadow registers will be updated also.

Nima

0 Colombo Carlo over 7 years ago in reply to Nima Eskandari

TI__Mastermind 24640 points

Hi Nima ,
thank you but I cannot wait and need to load before ( my issue is " immediate" is causing as said some complete 1 or complete 0 period i m still investigating why ...)
in my case I have 4 pwms 90 degrees one to the other @ 10Khz with 2 uS deadtime .
all of them must have same duty and I must update value every 2.5uS ( CLA working @ 400KHz )
so what i need is :
-load CMP registers ( shadowed mode )
-load the value on command in active register not waiting for TBPRD or TBzero .

any suggestion / idea ?
best regards
Carlo

0 Nima Eskandari over 7 years ago in reply to Colombo Carlo

TI__Guru 52040 points

Is forcing a SW sync an option? If you force a SW sync the counter will reset and the update will take place.

Nima

0 Colombo Carlo over 7 years ago in reply to Nima Eskandari

TI__Mastermind 24640 points

HI NIma ,
it is not , I must not reset the counter . I need only to update the compare reg .
thank you
regards
Carlo

0 Nima Eskandari over 7 years ago in reply to Colombo Carlo

TI__Guru 52040 points

Carlo,

Okay thank you. Can you give me the following info so my answers aren't generic?

Are you using Up mode or up-down mode?

Nima

0 Nima Eskandari over 7 years ago in reply to Nima Eskandari

TI__Guru 52040 points

Also with the specifications you are giving me, it seems like you have to use immediate mode. I think I know why you get a full period of high or low. I think the issue is that you update your CMPA,B values using immediate mode, then since there is a phase shift, these values are not in the range between CTR and PRD, causing the AQ to never have an event for a period.

Nima

0 Colombo Carlo over 7 years ago in reply to Nima Eskandari

TI__Mastermind 24640 points

Hi Nama ,
i m in up/down . yes immediate is causing me issue .
any idea ?
thank you
regrads
Carlo

0 Nima Eskandari over 7 years ago in reply to Colombo Carlo

TI__Guru 52040 points

Can you read my message above and verify that isn't happening?

0 Colombo Carlo over 7 years ago in reply to Nima Eskandari

TI__Mastermind 24640 points

HI Nima ,
it worked! so we are on immediate and double checking not to be too close to reload points .
thank you very muhc
regards
Carlo

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TMS320F28374D: help on pwm compare registers load at a sync signal