LPC1114 General Purpose Timer - PWM

Create a new project with the structure shown below:

The timer.h and timer.c files are from the previous section.

Add declarations of two variables and two functions in timer.h, as shown below:

#ifndef __NXPLPC11xx_TIME_H__

#define __NXPLPC11xx_TIME_H__

extern uint16_t cycle;

extern uint8_t duty;

extern void T16B0_init(void);

extern void T16B0_delay_ms(uint16_t ms);

extern void T16B0_delay_us(uint16_t us);

extern void T16B0_cnt_init(void);

extern void T16B0_CAP_Init(void);

extern void T16B0M0_PWM_Init(void);

extern void T16B0M0_PWM_SET(void);

#endif

In the timer.c file, add two variables and two functions:

1. uint16_t cycle; // cycle, unit: microseconds

2. uint8_t duty; // duty cycle, range 1~99

3. void T16B0M0_PWM_Init(void)

4. {

5.    if((duty>=100)&&(duty<=0))return; //If the duty cycle value is not a number between 1 and 99, exit the function

6.    LPC_SYSCON->SYSAHBCLKCTRL |= (1<<7); //Enable TIM16B0 clock

7.    LPC_SYSCON->SYSAHBCLKCTRL |= (1<<16); // Enable IOCON clock

8.    LPC_IOCON->PIO0_8 &= ~0x07;

9.    LPC_IOCON->PIO0_8 |= 0x02; //Set P0.8 pin to MAT0

10.    LPC_SYSCON->SYSAHBCLKCTRL &= ~(1<<16); // Disable IOCON clock

11.    LPC_TMR16B0->TCR = 0x02; //Reset timer (bit 1: write 1 to reset)

12.    LPC_TMR16B0->PR = SystemCoreClock/1000000-1; //1 microsecond TC+1

13.    LPC_TMR16B0->PWMC= 0x01; //Set MAT0 as PWM output pin

14.    LPC_TMR16B0->MCR = 0x02<<9; //Reset TC when setting MR3 match, that is, use MR3 as period register

15.    LPC_TMR16B0->MR3 = cycle; //Set cycle

16.    LPC_TMR16B0->MR0 = cycle/100*(100-duty); //Set duty cycle

17.    LPC_TMR16B0->TCR = 0x01; //Start the timer

18. }

1. void T16B0M0_PWM_SET(void)

2. {

3.    if((duty>=100)&&(duty<=0))return; //If the duty cycle value is not a number between 1 and 99, exit the function

4.    LPC_TMR16B0->MR0 = cycle/100*(100-duty); //Set duty cycle

5. }

Lines 1 and 2 define two variables, namely period and duty cycle. The period unit is microseconds because in the following PWM initialization function, the TC increment time will be set to 1 microsecond.

Lines 3 to 18 define a PWM initialization function and set the PWM output pin to P0.8.

Line 14 sets MR3 as the period register.

Line 15, write cycle

Line 16, write the duty cycle value.

Lines 19 to 23 are the PWM duty cycle setting functions

Line 22, enter the duty cycle value

In the main.c file, enter the following code:

1. #include “lpc11xx.h”

2. #include “timer.h”

1. void delay_ms(uint16_t ms)

2. {

3.    uint16_t i,j;

1.    for(i=0;i<5000;i++)

2.       for(j=0;j

3. }

1. int main()

2. {

3.    cycle = 10000;

4.    duty = 99;

5.    T16B0M0_PWM_Init();

1.    while(1)

2.    {

3.       delay_ms(50);

4.       if(duty<50)duty=99;

5.       T16B0M0_PWM_SET();

6.       duty–;

7.    }

8. }

The main function defines a period of 10000 microseconds, or 100 Hz, and an initial duty cycle of 99. Then, in the while loop, the duty cycle is changed every 50 milliseconds, and the duty cycle changes cyclically from 99 to 50.

Take an oscilloscope and you can see a 100Hz signal on the P0.8 pin, with the duty cycle constantly changing from 99 to 50.

If you don't have an oscilloscope, you can connect the P0.8 pin to the pin connected to the LED, and you can see the changes in the brightness of the LED light.