TMS320F2803X Piccolo ePWM Module for 0% and 100% Duty Cycle Control

Hi Henry

Of course you can generate PWM without ISR's. The need for ISR's is usually defined by the system architecture - i.E. do you have a lot of other tasks to be served, is your PWM generation part of a time critical control loop, is there a need of priority scheduling....
But for simple PWM generation you can directly write into the respective registers. I suppose you to have a look into the examples provided with controlSUITE, there you can learn a lot about PWM generation!

Best regards

Andreas

I have been testing some configurations to generate a single PWM signal, but I have a problem when loading the CMPA value greater than the TBPRD value for the following configuration:

- Up-Down counter
- CMPA load on TBCTR = 0x0000
- CAD Force output LOW ( CMPA == TBCTR and Counter Decrementing)
- CAU Force output HI  ( CMPA == TBCTR and Counter Incrementing)
- CMPA register in shadow mode
- DeadBand disabled
- Forcing actions disabled
- TZ and DC compare actions disabled
- Chopper Disabled

During initialization the CMPA and TBCTR values are initialized to 0, so as soon as the module is activated the CAU Force output HI condition is met and the pin goes HI as expected.

After the initialization, for any value between 0 and PWM_PERIOD loaded into the CMPA, the PWM works as expected.

The situation that is not clear for me is when a value > PWM_PERIOD is loaded into CMPA:

i.e:

- At Initialization : TBPRD = PWM_PERIOD, CMPA = 0.
The output remains HI as expected, as the only condition being triggered is : CAU Force output HI (CMPA == TBCTR and Counter Incrementing)

if after Initialization CPMA is loaded with a value > PWM_PERIOD(I update the new value after 50ms) , lets say 11000, then the output signal goes LOW.
From my point of view it should not go LOW, as the only active  condition to force the output LOW is CAD ( CMPA == TBCTR and Counter Decrementing), and it's supossed that the TBCTR never reaches the CMPA value and the condition CMPA = TBCTR is not present according to:

SPRUGE9E–December 2008–Revised March 2011 TMS320x2802x, 2803x Piccolo Enhanced Pulse Width Modulator (ePWM) Module PAGE 44.

Table 12. Behavior if CMPA/CMPB is Greater than the Period


Probably I'm not understanding the datasheet or maybe there is a mistake on my Initialization process.
Could anybody please help me to understand what is the problem?


Here is my Initialization process:

#define PWM_PERIOD          10000U

Initialization:

void PWM_Init(void)
{
EALLOW;
SysCtrlRegs.PCLKCR0.bit.TBCLKSYNC = 0;
EDIS;

EPwm1Regs.TBCTL.bit.CTRMODE = 0x3;        // Disable the timer

EPwm1Regs.TBCTL.all = 0x0033;        // Sync Out Disabled, Disable the timer

EPwm1Regs.TBCTR = 0U;
EPwm1Regs.TBPRD = PWM_PERIOD;        // Set timer period
EPwm1Regs.TBPHS.half.TBPHS = 0x0000;    // Set timer phase

EPwm1Regs.CMPA.half.CMPA = 0U;        // Set PWM duty cycle
   
EPwm1Regs.CMPCTL.all = 0x0000;        // Shadow mode, load on zero match

EPwm1Regs.AQCTLA.all = 0x0060;        // Action-qualifier control register A
// bit 15-12     0000:   reserved
// bit 11-10     00:     CBD, 00 = do nothing
// bit 9-8       00:     CBU, 00 = do nothing
// bit 7-6       01:     CAD, 01 = clear       <---------
// bit 5-4       10:     CAU, 10 = set         <---------
// bit 3-2       00:     PRD, 00 = do nothing
// bit 1-0       00:     ZRO, 00 = do nothing


EPwm1Regs.AQSFRC.all = 0x0000;        // forcing disabled register

EPwm1Regs.AQCSFRC.all = 0x0000;        // forcing disabled register

EPwm1Regs.DBCTL.all = 0;            // Deadband disabled   
EPwm1Regs.DBRED = 0;
EPwm1Regs.DBFED = 0;   
   
EPwm1Regs.PCCTL.bit.CHPEN = 0;        // PWM chopper unit disabled
EPwm1Regs.TZDCSEL.all = 0x0000;        // TZ and DC compare actions disabled

EPwm1Regs.TBCTL.bit.CTRMODE = 0x2;        // Enable the timer in count up/down mode


EALLOW;
SysCtrlRegs.PCLKCR0.bit.TBCLKSYNC = 1U;    // TBCLK to ePWM modules enabled
EDIS;
}


Then after 50ms I just update the CMPA register like this:

EPwm1Regs.CMPA.half.CMPA = 11000;

Thanks,

Hi Andreas,

Thanks for your support.  Yes, I was misunderstanding the datasheet.

Anyway on the second column of the Table 12. Behavior if CMPA/CMPB is Greater than the Period it should be:

Compare on Up-Count Event
CAU/CBU

Instead of:

Compare on Up-Count Event
CAD/CBD

Right?

Best Regards,

Henry Abril said:

Anyway on the second column of the Table 12. Behavior if CMPA/CMPB is Greater than the Period it should be:

Compare on Up-Count Event
CAU/CBU

Yes that is a mistake in the Document!

Regards

Andreas