TMS320F28335: ePWM TZFRC does not work properly

Part Number: TMS320F28335

Hi,

I'm fairly new to the C2000 microcontrollers. I have a TMS320F28335 and want to use it to control my AC-DC converter. I struggle with the Trip-Zone Force Register (TZFRC). When an overvoltage or overcurrent is detected, my state machine should go to ERROR state and I want to force my ePWM signals to low. So I use the following code in my main file:

			case ERROR:
			    EALLOW;
			    // lock PWM output (force to low - all off)
			    EPwm1Regs.TZFRC.bit.OST=1;              //force a one-shot trip event via software (0 = ignore, 1 = trip event and set the TZFLG[OST] bit)
			    EPwm2Regs.TZFRC.bit.OST=1;
			    EPwm3Regs.TZFRC.bit.OST=1;
			    EPwm4Regs.TZFRC.bit.OST=1;
				EPwm5Regs.TZFRC.bit.OST=1;
				EPwm6Regs.TZFRC.bit.OST=1;				
				EDIS;
				STOP;
			break;

In another file I initialize my ePWM registers as follows:

void PWMInit()
{

	//----------------------
	// Configuration
	//----------------------
	Uint16 DT = DEAD_TIME*c_CPUFRQ;						// c_CPUFRQ in MHz, Dead_time in us

	EALLOW;												// Allow to access registers
	SysCtrlRegs.PCLKCR0.bit.TBCLKSYNC = 0;      		// Stop all the TB clocks
	EDIS;												// Lock Registers

	// EPWM Module 1 config
	EPwm1Regs.TBPRD = MOD_HALF_CYCLE; 					// Period = 7500 TBCLK counts (PWM period = 100us)  @ 150 MHz
	EPwm1Regs.TBPHS.half.TBPHS = 0; 					// Set Phase register to zero
	EPwm1Regs.TBCTL.bit.CTRMODE = TB_COUNT_UP; 		    // Asymmetrical mode
	EPwm1Regs.TBCTL.bit.PHSEN = TB_DISABLE; 			// Master module
	EPwm1Regs.TBCTL.bit.PRDLD = TB_SHADOW;				// Shadow Register
	EPwm1Regs.TBCTL.bit.SYNCOSEL = TB_CTR_ZERO; 		// Sync down-stream module
	EPwm1Regs.TBCTL.bit.CLKDIV = TB_DIV1;				// No pre-scaling
	EPwm1Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1;			// No pre-scaling
	EPwm1Regs.CMPCTL.bit.SHDWAMODE = CC_SHADOW;
	EPwm1Regs.CMPCTL.bit.SHDWBMODE = CC_SHADOW;
	EPwm1Regs.CMPCTL.bit.LOADAMODE = CC_CTR_ZERO; 	//CC_CTR_ZERO; 	// Active Counter-Compare A (CMPA) Load From Shadow Select Mode. Load on CTR = Zero (TBCTR = 0x0000).
	EPwm1Regs.CMPCTL.bit.LOADBMODE = CC_CTR_ZERO; 	//CC_CTR_ZERO; 	// Load on CTR = Zero
   	// Set up Action Qualifier regs (AQ)
    EPwm1Regs.AQCTLA.bit.ZRO = AQ_CLEAR;
    EPwm1Regs.AQCTLA.bit.CAU = AQ_SET;

	// Set up Dead Band regs (DB)
	EPwm1Regs.DBCTL.bit.OUT_MODE = DB_FULL_ENABLE;  	// Enable Dead-band module
	EPwm1Regs.DBCTL.bit.POLSEL = DB_ACTV_HIC;           // Active high complementary  mode. EPWMxB is inverted
	EPwm1Regs.DBCTL.bit.IN_MODE = DBA_ALL;

	EPwm1Regs.DBFED = DT; 								// FED =  TBCLKs = 0.1us @ 150 MHz
	EPwm1Regs.DBRED = DT; 								// RED =  TBCLKs = 0.1us @ 150 MHz

	// Set up Trip Zone regs (TZ)
   	EPwm1Regs.TZCTL.bit.TZA	= TZ_FORCE_LO;				// Force to low at trip
   	EPwm1Regs.TZCTL.bit.TZB	= TZ_FORCE_LO;				// Force to low at trip
   	EPwm1Regs.TZFRC.bit.OST=1;

All other registers are initialized alike. However, my signals are not forced to low, I measure 0.4V for them. I also tried to force them high by setting "EPwm1Regs.TZCTL.bit.TZB    = TZ_FORCE_HI;", which also results in those 0.4V. So something is clearly not working properly.

If I write "EPwm1Regs.TZCTL.bit.TZA = TZ_FORCE_LO;" (or HI) directly into the main file, I do get 0V (or 3.3V) as expected, so I do know that the transition into ERROR state is working properly. So my question remains why the TZFRC is not working properly? I had a look at the technical reference manual. There would also be the TZSEL and TZEINT registers that I could use. I think in my case I do not need the TZSEL register as I use a software forced trip-zone? But maybe the TZEINT? Where would I put that, with the initialization (before or after the TZCTL lines?) or in the main file?

Also, in the initialization, do I need the last line "EPwm1Regs.TZFRC.bit.OST=1;" or is it enough if I use that in the main file?

Thanks!