Hi
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)
{
}
}
