TMS320F28335: Deadband in rising & Falling edge using Ecap/APWM

Hi Arsalan,

I understand you would like to apply a deadband to the ECAP. However, I believe you could do exactly what you are trying to do with using the EPWM module. Is there a reason you're not using the EPWM?

When applying a deadband to the ecap, it will only be possible with some software intervention. Here is a thread that might be able to help you,

Best,

Ryan Ma

Hi Ryan,

Thanks for your reply.

Is there any possibility that I can capture the signal (generator) and then generate PWM signals using EPWM module for the captured signal not through using APWM(from Ecap)?  Actually, I saw the lab example (7_6) which uses the deadband feature and generates PWM signals from the EPWM module (code below) but it doesn't capture the signal. That's why I started initially with Ecap module.  

Code=>

{
EPwm1Regs.TBCTL.bit.CLKDIV = 0; // CLKDIV = 1
EPwm1Regs.TBCTL.bit.HSPCLKDIV = 1; // HSPCLKDIV = 2
EPwm1Regs.TBCTL.bit.CTRMODE = 2; // up - down mode

EPwm1Regs.AQCTLA.all = 0x0060; // set ePWM1A on CMPA up
// clear ePWM1A on CMPA down

EPwm1Regs.AQCTLB.all = 0x0600; // set ePWM1B on CMPB up
// clear ePWM1B on CMPB down
EPwm1Regs.TBPRD = 37500; // 1KHz - PWM signal

EPwm1Regs.CMPA.half.CMPA = EPwm1Regs.TBPRD / 2; // 50% duty cycle first
EPwm1Regs.CMPB = EPwm1Regs.TBPRD / 2;

EPwm1Regs.DBRED = 750; // 10 microseconds delay
EPwm1Regs.DBFED = 750; // for rising and falling edge
EPwm1Regs.DBCTL.bit.OUT_MODE = 3; // ePWM1A = RED
EPwm1Regs.DBCTL.bit.POLSEL = 2; // S3=1 inverted signal at ePWM1B
EPwm1Regs.DBCTL.bit.IN_MODE = 0; // ePWM1A = source for RED & FED
}

Can you please suggest how can I relate this above code to my Ecap code? I guess I need to pass the values of Period into my EPwm1Regs.TBPRD. Like this=>

 EPwm1Regs.TBPRD = PWM_Period; ( variable multiply any factor for period settings if required)---for Period

EPwm1Regs.CMPA.half.CMPA  = PWM_Duty; (variable multiply any factor for duty settings if required)--- for Duty cycle

Is this the right way that I could generate 2 EPWMs signals for my captured ECap signal (GPIO24)  i.e EPW1A & EPWM1B-inverted with deadband setting(as mentioned above deadband setting code) ???  

Note: I should active the MUX for EPWM1A & EPWM1B as well in my GPIO select

Please review the code & suggest accordingly

Thanks

Regards

Arsalan

Hi Arsalan,

You're on the right path, instead of setting the period and duty cycle for the apwm. You can instead set the epwm.TBPRD register to the ecap's captured period, and set the CMPA register equal to ECAP's duty cycle. The deadband must be set using the dead band registers:

EPwm1Regs.DBRED = 750; // 10 microseconds delay
EPwm1Regs.DBFED = 750; // for rising and falling edge

There are also many resources to learn about epwm features:

1. Training videos

2. C2000 Academy page

3. App Note

Best,

Ryan Ma

Hi Ryan,

I tested the code today and reviewed the resources that you shared. Also, I followed the same process for TBPRD and the compare values in my last code but I didn't get the results from GPIO0(ePWM1A) & GPIO01(ePWM1B). Secondly, the register is 16-bit for TBPRD in ePWM but for PWM_Period/Duty is 32-bit which can cause an issue.  

Then I changed the function eCap before ePWM to keep the order first for eCap for capturing the signal from the generator and then produce ePWM for the captured results, this change in function is done like this =>

void Setup_eCAP1(void);
void Setup_ePWM1(void);

.......................

Setup_eCAP1(); // init eCAP1

Setup_ePWM1(); // init ePWM1

Still having no output. 

Here are the updates for the outputs and all four registers eCap1,eCap2,eCap3 and ePWM1(A&B):

Before providing the signal at GPIO24(Ecap1) from the generator, the values of the registers and output (epWM1A-GPIO0, ePWM1B-GPIO1) are shown here =>

After giving signals at GPIO24(Ecap1) from the generator, the output (epWM1A-GPIO0, ePWM1B-GPIO1), and the register values are shown below: 

After some delay, no signal at the output (epWM1A-GPIO0,ePWM1B-GPIO1) and the registers values are =>

Please review the code accordingly

Looking forward to your feedback

Thanks

Regards

Arsalan

Hi Arsalan,

In the last screenshot you sent your TBPRD is less than your CMPA value. I assume the action qualifier event never gets reached and your action qualifier will not take affect on the output. Try and set your CMPA value to be less than your period. 

I would also make sure to enable PUD for GPA

    GpioCtrlRegs.GPAPUD.bit.GPIO0 = 0;    // Enable pull-up on GPIO0 (EPWM1A)
    GpioCtrlRegs.GPAPUD.bit.GPIO1 = 0;    // Enable pull-up on GPIO1 (EPWM1B)   
    GpioCtrlRegs.GPAMUX1.bit.GPIO0 = 1;   // Configure GPIO0 as EPWM1A
    GpioCtrlRegs.GPAMUX1.bit.GPIO1 = 1;   // Configure GPIO1 as EPWM1B

You're correct, the TBPRD is 16 bits. Will you need a signal that needs to have a period that is equal to 2^32? This would mean a max period of 28.6s.

Also note that TBCLK has two dividers and default will divide SYSCLKOUT by /2. (HSPCLKDIV). 

ECAPCLK is clocked by sysclk, and thus you would have to divide your Period/counter values by 2 so they are at the same sysclk. 

Also, ECAP APWM is technically a PWM signal, in up count mode where CAP1 is the period and CAP2 is the duty cycle (CMPA). 

Best,

Ryan Ma

Hi Ryan,

Thanks for your reply. 

In the last screenshot you sent your TBPRD is less than your CMPA value. I assume the action qualifier event never gets reached and your action qualifier will not take affect on the output. Try and set your CMPA value to be less than your period. 

For this part, in previous posts pictures CMPA/CMPB both are greater than TBPRD when I wrote PWM_Duty (EPwm1Regs.CMPA.half.CMPA = PWM_Duty;). Therefore, Instead of writing PWM_Duty, I write the code like this in EPwm1Regs.TBPRD/2 form=>

EPwm1Regs.TBPRD = PWM_Period; // 1KHz - PWM signal

EPwm1Regs.CMPA.half.CMPA = (EPwm1Regs.TBPRD) / 2; // 50% duty cycle first
EPwm1Regs.CMPB = (EPwm1Regs.TBPRD) / 2;

In this way, see the Registers. CMPA & CMPB becomes half...for 50% duty cycle. (Now it becomes half of TBPRD).

Secondly, the TBPRD doesn't change whether you apply 1KHz or 120Khz, see the registers. Even also it doesn't change before the signal is applied from the generator and after applying and then waiting for some delay. TBPRD doesn't show any change in values. 

Also, ECAP APWM is technically a PWM signal, in up count mode where CAP1 is the period and CAP2 is the duty cycle (CMPA).

I have also tried this by writing for this part (for line: EPwm1Regs.TBPRD = PWM_Period; // 1KHz - PWM signal) like this way =>

EPwm1Regs.TBPRD = Ecap2Regs.CAP3; (or Ecap2Regs.CAP1)..... But this TBPRD doesn't change whatever the freq you apply. See the Registers please.

I would also make sure to enable PUD for GPA

Also this part, but didn't make any impact as well.

Also note that TBCLK has two dividers and default will divide SYSCLKOUT by /2. (HSPCLKDIV). 

ECAPCLK is clocked by sysclk, and thus you would have to divide your Period/counter values by 2 so they are at the same sysclk

For this part, when I used the prescaler divided by 2 (through ECap1Regs.ECCTL.PRESCALER (00001), this reduces the freq of my generator applied signal by half like (60Khz for 120Khz) which i don't want. So I kept at PRESCALER(00000). To set the sysclk same, I used the HSPCLKDIV = 0 (no division) and CLKDIV = 0 in EPWM code to keep the sysclk same with Ecapclk.  Still having no response. 

You're correct, the TBPRD is 16 bits. Will you need a signal that needs to have a period that is equal to 2^32? This would mean a max period of 28.6s.

I guess i am copying the values of 32 bit (PWM_Period) into TBPRD (16bit) which is not updating the TBPRD values.  In short, TBPRD must change accordingly with PWM_Period ( depending upon the generator signal freq) which seems not working. Please suggest in code:

Before applying signals from the generator =>

After applying 120Khz signal from the generator =>

Looking forward for your reply

Thanks 

Arsalan

Hi Arsalan,

Could you show me the PWM_Period value when it's calculated? You will need to use that number and convert it to find what your TBPRD value will need to be.

The TBPRD value can be calculated using this formula from the TRM

Hi Ryan,

It is shown in the picture of register values in my last post. PWM_Period & PWM2_ Period are same 1250 and the duty cycle is 625 (PWM_duty / PWM2_duty).

Hi Arsalan,

I believe your peripheral is not enabled so there is no output occurring.

Verify this is within your InitSysCtl() that epwm peripheral is enabled.

    EALLOW;
    SysCtrlRegs.PCLKCR0.bit.TBCLKSYNC = 0;
    EDIS;
    Setup_ePWM1();     // init  ePWM1A
    EALLOW;
    SysCtrlRegs.PCLKCR0.bit.TBCLKSYNC = 1;
    EDIS;

Also make sure to write this before your while loop within your main body of code.

I would also set the period to some default value at the beginning where you initialize your EPWM to see if the pwm does output something.

Best,

Ryan Ma

Also are you using the controlCARD TMDSCNCD28335?

EPWM1A would be on GPIO-00 -> pin 23 on that board

Hi Ryan,

Thanks for your reply.

I believe your peripheral is not enabled so there is no output occurring.

Verify this is within your InitSysCtl() that epwm peripheral is enabled.

Also make sure to write this before your while loop within your main body of code.

I would also set the period to some default value at the beginning where you initialize your EPWM to see if the pwm does output something.

Also are you using the controlCARD TMDSCNCD28335?

EPWM1A would be on GPIO-00 -> pin 23 on that board

Answer :

For this part, the peripheral is enabled because when you give a value like 37500 (for 2Khz... EPwm1Regs.TBPRD =  37500; ) instead of writing PWM_Period(32bit), you will get the PWM signals with 50% duty cycle at oscilloscope (Please see Picture1, Picture2) no matter either you close the eCap module function or not in the code. So it means there is no issue in the peripheral enable.

Also, there is no issue with InitSystrl() function because I am using a DSP2833x_Sysctrl.c which already shows that epwm peripheral is open: => (see in the code Picture3): and the code is also written before while loop in the main function of my code(code_attached).

Also, it is GPIO00 at the peripheral board Docking station that takes the control card inside in J1 headers (Pin 23 is for the control card pin not for peripheral board pins) because I have tested previous simple PWM programs labs from TI lab examples before with this GPIO00 port by changing TBPRD, Dead time and duty cycle etc. For satisfaction I checked GPIO23(pin23) once at the peripheral board doesn't give anything. So it's GPIO00 & GPIO01 where you can get EPWM1A & EPWM1B signals exactly. 

Picture3 (for DSP2833x_Sysctrl.c)

Picture1

Picture2

The Problem 1

I see that when you give 75000 (for 1Khz value EPwm1Regs.TBPRD =  75000;) then you see in the register and warnings like:  "70-D integer conversion resulted in truncation". (See Picture4). The TBPRD register shows an incorrect value due to this truncation error (See Picture 4).

Note : Smaller Values like 37500(2Khz) or 18750(4KHz) or 1250(120Khz). the TBPRD registers are showing correct values and the results are visible at the oscilloscope in the form of EPWM signals (no warning sign of truncation error). 

Picture 4 (Truncation warning when TBPRD = 75000) and the TBPRD register values are incorrect).

The Problem 2

When you replace the TBPRD numbers(75000,37500,18750..1250(120Khz)... etc) with the variable PWM_Period (32bit) for my Ecap signal module, then your TBRD value doesn't update itself. So it means it doesn't detect the variable when you see the register values in picture 5.

Picture 5

Please suggest and review the code such that the variable PWM_Period(32bit)/PWM_duty(32bit) can work.

Looking forward to your reply.

Thanks 

Arsalan

Hi Arsalan,

It seems that your epwm1 is not loading the shadow to active register when no write to the TBPRD is happening.

Within your ECAP interrupt try and set the TBPRD to the updated period value.

Best regards,

Ryan Ma 

Hi Ryan,

Thanks for your reply.

Within your ECAP interrupt try and set the TBPRD to the updated period value.

It means that,

should I assign the TBPRD value in the interrupt block ??? Like this =>

interrupt void eCAP1_isr(void)
{
ECap1Regs.ECCLR.bit.INT = 1; // Clear the ECAP1 interrupt flag
- 
-

-

ECap1Regs.ECCTL2.bit.REARM = 1;

EPwm1Regs.TBPRD = PWM_Period; // number- 75000,37500,18750..etc

PieCtrlRegs.PIEACK.all = PIEACK_GROUP4; // Must acknowledge the PIE group 4
}

then ePWM1 function - - - void Setup_ePWM1(void) { ---CLK, Action Qualifier, (no TBRD in this function), CMP, Deadband,  - - - - }

Can I try this way?

Thanks

Regards

Arsalan

Hi Ryan,

Finally, the Deadband feature (rising and falling edges) is resolved now. Thanks. I will post another thread for the phase shift of 180 degree between EPWM1A & EPWM1B.

Thanks Ryan

Hi Arsalan,

Glad to hear you got these features working :) 

Best of luck in your work!