need 0 to 100 % pwm generation on tiva 123g development board

krish50197

I am trying to generate a pwm signal of 25khz period. and 0 to 100% duty cycle variation. But i do not see 0-100% variation in pwm duty cycle. the duty cycle and pulse width count relation is 0% - 170 , 66% - for 400 and above.

Below is the code. I have used the code from the example.. I change the pulse width count manually for now.

void main(void)

{

uint32_t period;

// Set the clocking to run directly from the external crystal/oscillator.

// TODO: The SYSCTL_XTAL_ value must be changed to match the value of the

// crystal on your board.

SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN |

SYSCTL_XTAL_16MHZ);

//SysCtlClockSet(SYSCTL_SYSDIV_16 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ | SYSCTL_OSC_MAIN);

// Set the PWM clock to the system clock.

SysCtlPWMClockSet(SYSCTL_PWMDIV_1);

// The PWM peripheral must be enabled for use.

SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);

// For this example PWM0 is used with PortB Pins 6 and 7. The actual port

// and pins used may be different on your part, consult the data sheet for

// more information. GPIO port B needs to be enabled so these pins can be

// used.

// TODO: change this to whichever GPIO port you are using.

SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOH);

// Configure the GPIO pin muxing to select PWM functions for these pins.

// This step selects which alternate function is available for these pins.

// This is necessary if your part supports GPIO pin function muxing.

// Consult the data sheet to see which functions are allocated per pin.

// TODO: change this to select the port/pin you are using.

GPIOPinConfigure(GPIO_PH0_M0PWM0);

// Configure the GPIO pad for PWM function on pins PB6 and PB7. Consult

// the data sheet to see which functions are allocated per pin.

// TODO: change this to select the port/pin you are using.

GPIOPinTypePWM(GPIO_PORTH_BASE, GPIO_PIN_0);

// Configure the PWM0 to count up/down without synchronization.

// Note: Enabling the dead-band generator automatically couples the 2

// outputs from the PWM block so we don't use the PWM synchronization.

PWMGenConfigure(PWM0_BASE, PWM_GEN_0, PWM_GEN_MODE_UP_DOWN |

PWM_GEN_MODE_NO_SYNC);

// Set the PWM period to 250Hz. To calculate the appropriate parameter

// use the following equation: N = (1 / f) * SysClk. Where N is the

// function parameter, f is the desired frequency, and SysClk is the

// system clock frequency.

// In this case you get: (1 / 250Hz) * 16MHz = 64000 cycles. Note that

// the maximum period you can set is 2^16 - 1.

// TODO: modify this calculation to use the clock frequency that you are

// using.

PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, 504);

// Set PWM0 PD0 to a duty cycle of 25%. You set the duty cycle as a

// function of the period. Since the period was set above, you can use the

// PWMGenPeriodGet() function. For this example the PWM will be high for

// 25% of the time or 16000 clock cycles (64000 / 4).

PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0,

250);

// Enable the dead-band generation on the PWM0 output signal. PWM bit 0

// (PD0), will have a duty cycle of 25% (set above) and PWM bit 1 will have

// a duty cycle of 75%. These signals will have a 10us gap between the

// rising and falling edges. This means that before PWM bit 1 goes high,

// PWM bit 0 has been low for at LEAST 160 cycles (or 10us) and the same

// before PWM bit 0 goes high. The dead-band generator lets you specify

// the width of the "dead-band" delay, in PWM clock cycles, before the PWM

// signal goes high and after the PWM signal falls. For this example we

// will use 160 cycles (or 10us) on both the rising and falling edges of

// PD0. Reference the datasheet for more information on dead-band

// generation.

PWMDeadBandEnable(PWM0_BASE, PWM_GEN_0, 160, 160);

PWMOutputState(PWM0_BASE, PWM_OUT_0_BIT, true);

// Enables the counter for a PWM generator block.

PWMGenEnable(PWM0_BASE, PWM_GEN_0);

// Loop forever while the PWM signals are generated.

while(1)

{

}

over 11 years ago

0 Luis Afonso over 11 years ago

Guru 20670 points

Hi,

Try not using the PWMDeadBandEnable(PWM0_BASE, PWM_GEN_0, 160, 160);

0 Petrei over 11 years ago in reply to Luis Afonso

Guru 26105 points

Hi,

Worth to know - strictly 0% and 100% cannot be obtained, not with this micro, neither with other brands. Usually, at these strict levels, other brands implement no waveform output, but static level either low or high.

You must maintain a small margin, 1..3 bits from these levels.

Petrei

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need 0 to 100 % pwm generation on tiva 123g development board