# What is the minimum frequency we can get in SCT 16 bit counter

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## What is the minimum frequency we can get in SCT 16 bit counter

669 Views
Contributor III

Hi,

I need to generate 0.5hz[with SCTtimer sample code] frequency in lp845 controller, with the sample code using

16 bit counter SCT, least frequency i'm getting is 0.9hz, not getting lesser then this,

how to get 0.5hz ,kindly advice, below is the calculation done:

For 30Mhz clock-->500[count value] * 30Mhz[sctimer clock] /1000 = 15Mhz

So for say 3hz its = 15M/3 = 5000000[this value is substituted in matchvalue]

Similarly for 0.5hz...but not getting as expected..suggest me is the above method

is correct and how to get 0.5hz using scttimer counter.

Thank you

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• ### LPC800

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5 Replies
518 Views
NXP TechSupport

Hi, Angiey,

From theory, the SCTimer is a clock divider, if you use 30MHz system clock, and set the UNIFY bit in SCTimer/PWM configuration register, the counter is 32bits counter, the divider is 2**32, you can get at least 30MHz/(2**32) =0.007Hz signal. So it is okay to get 0.5HZ signal if you set the match register as 60 000 000.

As an alternative, you can use input 4 as the SCTimer clock signal, which can be 12MHz FRO, but you have to use 32bits counter by setting the UNIFY bit in SCTimer/PWM configuration register.

BR

XiangJun rong

518 Views
Contributor III

Hi,

By default SCTtimer configuration was in 16 bit so for 32 bit the boolean

value is *true *and set the

match register to 60000000 but still not getting the 0.5hz signal,

is there any other configuration to be changed.

Thank you

On Mon, Jul 15, 2019 at 1:56 PM xiangjun.rong <admin@community.nxp.com>

518 Views
NXP TechSupport

Hi, Angiey,

This is an example code I copied from SDK.

SCTIMER_GetDefaultConfig(&sctimerInfo);

sctimerInfo.enableCounterUnify = true; /* SCT operates as a unified 32-bit counter */

/* Initialize SCTimer module */
SCTIMER_Init(SCT0, &sctimerInfo);

/* Configure first PWM with frequency 1HZ from first output */
pwmParam.output = DEMO_FIRST_SCTIMER_OUT;
pwmParam.level = kSCTIMER_HighTrue;
pwmParam.dutyCyclePercent = 50;
if (SCTIMER_SetupPwm(SCT0, &pwmParam, kSCTIMER_CenterAlignedPwm, 1U, sctimerClock, &event) == kStatus_Fail)
{
return -1;
}

If you use above code, can you get 1HZ PWM signal?

If you can get 1HZ PWM signal, you can use the code to get 0.5HZ PWM signal I suppose.

/* SCT operates as a unified 32-bit counter */

if (SCTIMER_SetupPwm(SCT0, &pwmParam, kSCTIMER_CenterAlignedPwm, 1U, 2*sctimerClock, &event) == kStatus_Fail)
{
return -1;
}

BR

Xiangjun Rong

518 Views
Contributor III

Thanks for the response..I tried with the above changes but not getting the

require frequency of 0.5hz, with the reference of SDK code tried initially by

changing the configuration of unifiy bit to 32 bit counter too,I have attach the

latest change code, is anything need to be changed..?kindly suggest on this.

void SCT_Detection_Callback(void)
{
GPIO_PortToggle(GPIO, BLUE_LED_PORT, 1u << BLUE_LED_PIN);
widths = SCT0->COUNT;

SCT0->CTRL |= (1<<19);//clear counter

uint32_t CTRL_Enable_Event = SCT0->CTRL;
CTRL_Enable_Event &= (~(SCT_CTRL_HALT_H_MASK) ); //clear halt H bit
CTRL_Enable_Event |= SCT_CTRL_STOP_H_MASK; //set stop H bit
//   SCT0->CTRL = CTRL_Enable_Event; //Write both changes at once
}

/*******************************************************************************
* Code
******************************************************************************/
/*!
* @brief Main function
*/
int main(void)
{
sctimer_config_t sctimerInfo;
uint32_t stateNumber;
uint32_t eventCounterL, eventCounterH;
uint32_t sctimerClock;
uint32_t matchValueL, matchValueH;

/* Board pin, clock, debug console init */

/* attach 12 MHz clock to FLEXCOMM0 (debug console) */
CLOCK_Select(BOARD_DEBUG_USART_CLK_ATTACH);

BOARD_InitPins();
BOARD_BootClockFRO30M();
BOARD_InitDebugConsole();

gpio_pin_config_t led_config = { kGPIO_DigitalOutput, 0, };
GPIO_PortInit(GPIO, BLUE_LED_PORT);
GPIO_PinInit(GPIO, BLUE_LED_PORT, BLUE_LED_PIN, &led_config);

if(SysTick_Config(SystemCoreClock / 100000U))
{
while(1)
{
}
}

LCD_Init();
LCD_Cmd(_LCD_CURSOR_OFF);
LCD_Cmd(_LCD_CLEAR);

sctimerClock = SCTIMER_CLK_FREQ;

/* Default configuration operates the counter in 32-bit mode */
SCTIMER_GetDefaultConfig(&sctimerInfo);

/* Switch to 16-bit mode */
sctimerInfo.enableCounterUnify = true ;//true[for 32 bit]
sprintf(txta, "%d ", sctimerInfo.enableCounterUnify);
LCD_Out(1,1,txta);

/* Calculate prescaler and match value for Counter L for 100ms interval */
matchValueL = MSEC_TO_COUNT(500U, sctimerClock);//changed values
sprintf(txtb, "%d ", matchValueL);
LCD_Out(2,1,txtb);

sctimerInfo.prescale_l = matchValueL / 65536;

matchValueL = matchValueL / (sctimerInfo.prescale_l + 1) - 1;

/* Calculate prescaler and match value for Counter H for 200ms interval */
matchValueH = MSEC_TO_COUNT(500U, sctimerClock);//changed values
sctimerInfo.prescale_h = matchValueH / 65536;
matchValueH = matchValueH / (sctimerInfo.prescale_h + 1) - 1;

/* Initialize SCTimer module */
SCTIMER_Init(SCT0, &sctimerInfo);

stateNumber = SCTIMER_GetCurrentState(SCT0);

/* Schedule a match event for Counter L every 0.1 seconds */
if (SCTIMER_CreateAndScheduleEvent(SCT0, kSCTIMER_MatchEventOnly, matchValueL, 0, kSCTIMER_Counter_L,
&eventCounterL) == kStatus_Fail)
{
return -1;
}

/* Toggle first output when Counter L event occurs */
SCTIMER_SetupOutputToggleAction(SCT0, DEMO_FIRST_SCTIMER_OUT, eventCounterL);

/* Reset Counter L when Counter L event occurs */
SCTIMER_SetupCounterLimitAction(SCT0, kSCTIMER_Counter_L, eventCounterL);

/* Schedule a match event for Counter H every 0.2 seconds */
if (SCTIMER_CreateAndScheduleEvent(SCT0, kSCTIMER_MatchEventOnly, matchValueH, 0, kSCTIMER_Counter_H,
&eventCounterH) == kStatus_Fail)
{
return -1;
}

/* Toggle second output when Counter H event occurs */
SCTIMER_SetupOutputToggleAction(SCT0, DEMO_SECOND_SCTIMER_OUT, eventCounterH);//P1.20 WONT TOGGLE

/* Reset Counter H when Counter H event occurs */
SCTIMER_SetupCounterLimitAction(SCT0, kSCTIMER_Counter_H, eventCounterH);

SCTIMER_SetCallback(SCT0, sctimer_callback_table, eventCounterH);//kSCTIMER_Counter_H

SCTIMER_EnableInterrupts(SCT0,1<<eventCounterH);//kSCTIMER_Counter_H

NVIC_EnableIRQ(SCT0_IRQn);

/* Start the timer, use counter L as we are operating counter in 32-bit mode */
SCTIMER_StartTimer(SCT0, kSCTIMER_Counter_L);//D6 PIN WONT TOGGLE
SCTIMER_StartTimer(SCT0, kSCTIMER_Counter_H);//D5 PIN WONT TOGGLE

while (1)
{
}
}

518 Views
NXP TechSupport

Hi,

The PWM code in SDK is complicated, I develop an example code for the 0.5HZ PWM signal, it is okay when I run it on LPC54114. You have to modify the code yourself based on your application.

BR

Xiangjun Rong

void SCT0_PWM_05Hz(void)
{
uint32_t clockDiv=2*SystemCoreClock;
SYSCON->AHBCLKCTRL[1]|=(1<<2); //SET SCT0 bit
SCT0->CONFIG = (1 << 0) | (1 << 17); // unified 32-bit timer, auto limit
SCT0->SCTMATCHREL[0] = clockDiv; // match 0 @ 100 Hz = 10 msec
SCT0->EVENT[0].STATE = 0xFFFFFFFF; // event 0 happens in all states

//set event1
SCT0->SCTMATCHREL[1]=0x00;
SCT0->EVENT[1].STATE = 0xFFFFFFFF; // event 1 happens in all states
SCT0->EVENT[1].CTRL = (1 << 12)|(1<<0); // match 1 condition only

//set event2
SCT0->SCTMATCHREL[2]=(clockDiv)/2;
SCT0->EVENT[2].STATE = 0xFFFFFFFF; // event 2 happens in all states
SCT0->EVENT[2].CTRL = (1 << 12)|(2<<0); // match 2 condition only

//set event3
SCT0->SCTMATCHREL[3]=(clockDiv)/4;
SCT0->EVENT[3].STATE = 0xFFFFFFFF; // event 3 happens in all states
SCT0->EVENT[3].CTRL = (1 << 12)|(3<<0); // match 3 condition only

//set event4
SCT0->SCTMATCHREL[4]=3*(clockDiv)/4;
SCT0->EVENT[4].STATE = 0xFFFFFFFF; // event 4 happens in all states
SCT0->EVENT[4].CTRL = (1 << 12)|(4<<0); // match 4 condition only

//PWM output1 signal
SCT0->OUT[1].SET = (1 << 1); // event 1 will set SCT1_OUT0
SCT0->OUT[1].CLR = (1 << 2); // event 2 will clear SCT1_OUT0
SCT0->RES |= (3 << 2); // output 0 toggles on conflict

//PWM output2 signal
SCT0->OUT[2].SET = (1 << 3); // event 3 will set SCT1_OUT0
SCT0->OUT[2].CLR = (1 << 4); // event 4 will clear SCT1_OUT0
SCT0->RES = (3 << 4); // output 0 toggles on conflict

//PWM start
SCT0->CTRL &= ~(1 << 2); // unhalt by clearing bit 2 of the CTRL
}