Problem scoping PWM with frequency 50Hz from F28069

Hello David,

   Thank you so  much for your reply.  I have got the error while building, but I declared the type PERIOD by Uint 16, thinking it would exceed the range. The error didnt occur later. But I still cannot get pulse wave at all frequencies.

Actually I want to generate pulse wave at all frequencies by giving the % of the duty cycle in GUI for a 20 ms wave Therefore, I set my CMPx to 0 initially.

I would be glad if you help me sole this problem.

Regards-

Prathamesh

Prathamesh,

I'm not understanding exactly what problem you are having.  What are you referring to when you say "GUI?"

If you set CMPX to zero, you will not see a PWM pulse.  The pin will be either high, or low, all the time (depends on how you have the ePWM module configured).

Set TBPRD=0xFFFF and CMPRx=0x8000.  This will generate a 50/50 PWM signal at the slowest frequency you can (without scaling the input clock to the ePWM module).  You should see the waveform on the scope.

- David

Hello David,

Actually, I need to control a motor that has  pulse duration  from 0.9mS to 2.1mS with 1.5mS as center. The pulse refreshes at 50Hz (20mS). I dont want to used deadband as it gives complimentry outputs. What can I do??

Regards-

Prathamesh

Hello David,

Thank you for your reply. I have  understood what you suggested. But I can only see the smallest prescalers as 1/4, thats TB_DIV4. How can I set it to 1/16?

Regards-

Prathamesh

Prathamesh,

I'm not seeing where the confusion is.  Look in the F2806x User's Guide, SPRUH18C, p.332, Table 3-29.  Set TBCTL.CLKDIV=100b for /16.

David,

I have gone through it and I am just worried if  i have done it right.

EPwm6Regs.TBCTL.bit.CLKDIV = 100 

David,

Thank you for bearing with me. I am a newbie to microcontroller programming. 

Regards-

Prathamesh 

David,

I have done the coding for 5 pwms (a,b) for one frequency. Now I want to interface a servo motor which needs the specification I mentioned earlier. I have made the necessary corrections, but I am still getting undesirable output.

Here are the details:

// Function based in example code: SymmetricPWM-Main.c
void InitPWM6mode(void){

	// Setup PWMs in Up-Down-Count, Dual Edge Symmetric Waveform, With Independent
	// Modulation on EPWM2A and EPWM2B
	//
	//			- In order to change the PWM frequency, the user should change
	//			 the value of"period".
	//			- The duty-cycles can independently be adjusted by changing compare
	//			values (duty_cycle_A & duty_cycle_B) for ePWM2A and ePWM2B.
	//			- For further details, please search for the SPRU791.PDF
	//			(TMS320x28xx, 28xxx Enhanced Pulse Width Modulator Module) at ti.com


   #define period1 50000                         // 50Hz when PLL is set to 0x10 (80MHz)
//  #define period 40000						  // 100Hz when PLL is set to 0x10 (80MHz)
//      period 250   			    	      // 160kHz when PLL is set to 0x10 (80MHz)
//      period 500   			    	      // 80kHz when PLL is set to 0x10 (80MHz)

  // Time-base registers

   	EPwm6Regs.TBPRD = period1;       		   // Set timer period, PWM frequency = 1 / period
   	EPwm6Regs.TBPHS.all = 0;				   // Time-Base Phase Register
   	EPwm6Regs.TBCTR = 0;					   // Time-Base Counter Register
    EPwm6Regs.TBCTL.bit.PRDLD = TB_IMMEDIATE;  // Set Immediate load
    EPwm6Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; // Count-updown mode: used for symmetric PWM
	EPwm6Regs.TBCTL.bit.PHSEN = TB_DISABLE;	   // Disable phase loading
	EPwm6Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_DISABLE;
	EPwm6Regs.TBCTL.bit.HSPCLKDIV = 0x4;
	EPwm6Regs.TBCTL.bit.CLKDIV = 0x4;

   	// Setup shadow register load on ZERO

   	EPwm6Regs.CMPCTL.bit.SHDWAMODE = CC_SHADOW;
   	EPwm6Regs.CMPCTL.bit.SHDWBMODE = CC_SHADOW;
   	EPwm6Regs.CMPCTL.bit.LOADAMODE = CC_CTR_ZERO;	// load on CTR=Zero
   	EPwm6Regs.CMPCTL.bit.LOADBMODE = CC_CTR_ZERO;	// load on CTR=Zero

   	// Set Compare values

   	EPwm6Regs.CMPA.half.CMPA = 0;    				// Set duty 0% initially
   	EPwm6Regs.CMPB = 0;	            				// Set duty 0% initially

   	// Set actions

   	EPwm6Regs.AQCTLA.bit.CAU = AQ_SET;            // Set PWM2A on event A, up count
   	EPwm6Regs.AQCTLA.bit.CAD = AQ_CLEAR;          // Clear PWM2A on event A, down count

   	EPwm6Regs.AQCTLB.bit.CBU = AQ_SET;            // Set PWM2B on event B, up count
   	EPwm6Regs.AQCTLB.bit.CBD = AQ_CLEAR;          // Clear PWM2B on event B, down count

And here is the case where it calls the PWM6:

case 'L':                                               //PWM ID
	     	while(SciaRegs.SCIFFRX.bit.RXFFST == 0){}			//Wait for command
			dutyCycle = SciaRegs.SCIRXBUF.all *0.06 * maxDutyCycle_1;
		 	EPwm6Regs.CMPB = dutyCycle;
			break;
		default:

I dont know, what is the problem. Thank you.

Regards-

Prathamesh,

You did not say what the "Undesirable"  PWM behavior is, and honestly I'm not even sure what the PWM specification is that you say you mentioned earlier.  I took a quick look at the code you sent, and I see the following two lines:

    EPwm6Regs.TBCTL.bit.HSPCLKDIV = 0x4;
    EPwm6Regs.TBCTL.bit.CLKDIV = 0x4;

The first line applies a /16 divider to the PWM input clock.  The second line applies an additional /8 divider to the PWM input clock, giving you a total divider of /128.  Is that what you want?  I thought you wanted /16, which lines up with what your #define for PERIOD1:

     #define    period1   50000         // 50Hz when PLL is set to 0x10 (80MHz)

Regards,

- David