LPC1549, PWM on SCT0_7

jørgenbusch — Wed, 17 Aug 2016 09:20:00 GMT

Hi,

I'm having trouble getting a PWM signal on PIO1_14 (for SCT0_7)

Maybe it the some clock issue, however I'm not sure. I hope you might have a hint of somekind.

Below is code (as you can see it is using the library from lpc chip. )

Using embOS as operating system.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

#define SCT_PWM LPC_SCT0 /* Use SCT0 for PWM */

#define SCT_PWM_PIN_OUT 7 /* COUT0_7 Generate square wave */

#define SCT_PWM_OUT 0

void Init_and_start_PWM(void)

{

	Chip_SYSCTL_PowerDown(SYSCTL_POWERDOWN_SCTPLL_PD);
	Chip_Clock_SetSCTPLLSource(SYSCTL_PLLCLKSRC_MAINOSC);
	Chip_Clock_SetupSCTPLL(5,2);
	Chip_SYSCTL_PowerUp(SYSCTL_POWERDOWN_SCTPLL_PD);
	/* Wait for PLL to lock */
	while (!Chip_Clock_IsSCTPLLLocked()) {}

#define SCT_PWM_RATE 200000 /* PWM frequency 200 KHz */

Chip_SCTPWM_Init(LPC_SCT0);

Chip_SCTPWM_SetRate(LPC_SCT0, SCT_PWM_RATE);

	/* Enable SWM clock before altering SWM */
	Chip_Clock_EnablePeriphClock(SYSCTL_CLOCK_SWM);

Chip_SWM_EnableFixedPin(SWM_FIXED_SCT0_OUT7);

Chip_Clock_DisablePeriphClock(SYSCTL_CLOCK_SWM);

Chip_SCTPWM_SetOutPin(LPC_SCT0, SCT_PWM_OUT, SCT_PWM_PIN_OUT);

	/* Start with 50% duty cycle */
	Chip_SCTPWM_SetDutyCycle(LPC_SCT0, SCT_PWM_OUT, Chip_SCTPWM_PercentageToTicks(LPC_SCT0, 50));

Chip_SCTPWM_Start(LPC_SCT0);

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Starting the PWM (just above), I only measure the pin goes high, and there it stays. Breaking the code shows that the counters are running in SCT.

BR Jørgen Busch

Re: LPC1549, PWM on SCT0_7

jørgenbusch — Wed, 17 Aug 2016 11:49:30 GMT

The define SCT_PWN_OUT cannot be 0, it must be fx, 1.

Then it runs :-)

Chip_SCTPWM_SetOutPin(LPC_SCT0, SCT_PWM_OUT, SCT_PWM_PIN_OUT);

	/* Start with 50% duty cycle */
	Chip_SCTPWM_SetDutyCycle(LPC_SCT0, SCT_PWM_OUT, Chip_SCTPWM_PercentageToTicks(LPC_SCT0, 50));

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