PWM on TMS570 with variable Duty Cycle and Frequency

Hello Arif,

I have copied one of our NHET experts to walk you through what you will need to do in order to achieve the variable duty cycle. He should get back with you soon.

Arif,

This is a good post to start with and there are links to differnet implementations you can try.

http://e2e.ti.com/support/microcontrollers/hercules/f/312/p/284151/993495.aspx#993495

Hello Chuck, Hello David,

Thanks a lot for your responses.

I have examined the page you advised. On the other hand, I tried to generate a code through Halcogen and compile it in CCS. When I check the functions in het.c source code which is generated by halcogen, I see a function which I assume as what I am actually looking for.

To set duty cycle:

void pwmSetDuty(hetRAMBASE_t * hetRAM, uint32 pwm, uint32 pwmDuty) 

And to set period:

pwmSetSignal(hetRAMBASE_t * hetRAM, uint32 pwm, hetSIGNAL_t signal)

I am confused about the arguments of these functions. How should I determine the parameters of these functions to generate a pwm signal with a period and duty cycle I specify?

/** @fn void pwmSetDuty(hetRAMBASE_t * hetRAM, uint32 pwm, uint32 pwmDuty)
*   @brief Set duty cycle
*   @param[in] hetRAM Pointer to HET RAM:
*              - hetRAM1: HET1 RAM pointer
*              - hetRAM2: HET2 RAM pointer
*   @param[in] pwm Pwm signal:
*              - pwm0: Pwm 0
*              - pwm1: Pwm 1
*              - pwm2: Pwm 2
*              - pwm3: Pwm 3
*              - pwm4: Pwm 4
*              - pwm5: Pwm 5
*              - pwm6: Pwm 6
*              - pwm7: Pwm 7
*   @param[in] pwmDuty duty cycle in %.
*
*   Sets a new duty cycle on the given pwm signal
*/
/* SourceId : HET_SourceId_004 */
/* DesignId : HET_DesignId_004 */
/* Requirements : HL_SR366 */
void pwmSetDuty(hetRAMBASE_t * hetRAM, uint32 pwm, uint32 pwmDuty)
{
    uint32 action;
    uint32 pwmPolarity =0U;
    uint32 pwmPeriod = hetRAM->Instruction[(pwm << 1U) + 42U].Data + 128U;
    if(hetRAM == hetRAM1)
    {
        pwmPolarity = s_het1pwmPolarity[pwm];
    }
    else
    {
    }
    if (pwmDuty == 0U)
    {
        action = (pwmPolarity == 3U) ? 0U : 2U;
    }
    else if (pwmDuty >= 100U)
    {
        action = (pwmPolarity == 3U) ? 2U : 0U;
    }
    else
    {
        action = pwmPolarity;
    }

    hetRAM->Instruction[(pwm << 1U) + 41U].Control = ((hetRAM->Instruction[(pwm << 1U) + 41U].Control) & (~(uint32)(0x00000018U))) | (action << 3U);
    hetRAM->Instruction[(pwm << 1U) + 41U].Data = (uint32)((pwmPeriod * pwmDuty) / (uint32)100U) + 128U;
}


/** @fn void pwmSetSignal(hetRAMBASE_t * hetRAM, uint32 pwm, hetSIGNAL_t signal)
*   @brief Set period
*   @param[in] hetRAM Pointer to HET RAM:
*              - hetRAM1: HET1 RAM pointer
*              - hetRAM2: HET2 RAM pointer
*   @param[in] pwm Pwm signal:
*              - pwm0: Pwm 0
*              - pwm1: Pwm 1
*              - pwm2: Pwm 2
*              - pwm3: Pwm 3
*              - pwm4: Pwm 4
*              - pwm5: Pwm 5
*              - pwm6: Pwm 6
*              - pwm7: Pwm 7
*   @param[in] signal signal
               - duty cycle in %.
*              - period period in us.
*
*   Sets a new pwm signal
*/
/* SourceId : HET_SourceId_005 */
/* DesignId : HET_DesignId_005 */
/* Requirements : HL_SR367 */
void pwmSetSignal(hetRAMBASE_t * hetRAM, uint32 pwm, hetSIGNAL_t signal)
{
    uint32 action;
    uint32 pwmPeriod = 0U;
    uint32 pwmPolarity = 0U;
    float32 temp = 0.0F;

    if(hetRAM == hetRAM1)
    {
        temp = ((float32)signal.period * 1000.0F) / 1422.222F;
        pwmPeriod = (uint32)temp << 7U;
        pwmPolarity = s_het1pwmPolarity[pwm];
    }
    else
    {
    }
    if (signal.duty == 0U)
    {
        action = (pwmPolarity == 3U) ? 0U : 2U;
    }
    else if (signal.duty >= 100U)
    {
        action = (pwmPolarity == 3U) ? 2U : 0U;
    }
    else
    {
        action = pwmPolarity;
    }

    hetRAM->Instruction[(pwm << 1U) + 41U].Control = ((hetRAM->Instruction[(pwm << 1U) + 41U].Control) & (~(uint32)(0x00000018U))) | (action << 3U);
    hetRAM->Instruction[(pwm << 1U) + 41U].Data = (uint32)((pwmPeriod * signal.duty) / (uint32)100U) + 128U;
    hetRAM->Instruction[(pwm << 1U) + 42U].Data = pwmPeriod - 128U;
}

I'd love to hear an answer to this- I'm working on an application that needs to generate varied PWM signals according to external triggers, and so far I can't figure out quite what to do.

What do I pass to the C functions

void pwmSetDuty(hetRAMBASE_t * hetRAM, uint32 pwm, uint32 pwmDuty)

and

pwmSetSignal(hetRAMBASE_t * hetRAM, uint32 pwm, hetSIGNAL_t signal)

?

I've attached some code that I used to get the PWM working. I used pwmSetSignal to control the duty cycle and frequency, i'm not sure why they don't have a pwmSetFrequency function.

The pwm0_signal structure elements can be modified in the debugger window or by your application.

You may also find this post of interest.

http://e2e.ti.com/support/microcontrollers/hercules/f/312/p/344034/1204654.aspx#1204654

Jamie6888.sys_main.c

Hi everybody

I saw this post and... Im going to control 12 different motors with different duty cyles, depending on the response of the PI controller...

Why dont you check the reference manual? on the pages 725 and 765 comes how to do what you want, even example codes... using the ePWM... this is the case of the tms570ls1115 MCU but you could check on your MCUs and do something similar...

best regards

Mike