(转)CortexM3 (NXP LPC1788)之PWM

(转)CortexM3 (NXP LPC1788)之PWM
PWM即脉宽调制，可用于输出一定占空比的方波。LPC1788有两个PWM,每个PWM可以由6路的输出，PWM1~PWM6。下面介绍使用PWM0.1输出PWM波。

        1，PWM使用公共的PCLK，因此要配置系统时钟和外设时钟。之前的文章中有具体的时钟配置过程。

        2，使能PWM模块。配置外设功率配置寄存器PCONP，使能PWM0的时钟控制位。

        3，PWM0.1的输出管脚和P1_2管脚复用，因此要配置IOCON_P1_02寄存器，将其设置成PWM0.1的输出。

        4，设置PWM的脉冲宽度，基本的原理就是比较PWM定时器计数器TC和匹配寄存器MR中的值，如果匹配我们可以通过匹配控制寄存器MCR选择操作，如产生一个中断，复位TC，停止TC和预分频计数器PC且停止计数。匹配寄存器MR0通过在匹配是将计数器TC复位来控制PWM的周期频率。另一个匹配寄存器控制PWM沿的位置。如PWM0.1的输出，将使用MR0控制PWM的周期频率，MR1控制边沿的位置。

        5，最后是对于PWM的具体控制，配置PWM预分频寄存器PWMPR，该32位寄存器规定了PWM预分频计数的最大值，PWM预分频计数器寄存器PWMPC在每个PCLK上递增一次，当PWMPC和PWMPR值相等时,PWMTC的值会递增，而PWMPR在系一个PCLK周期被复位。这样，当PWMPR=0时，PWMTC会在每个PCLK上递增，而当PWMPR=1时，在每2个PCLK上递增。匹配寄存器PWMMR中的值和PWMTC的值比较，如果相等则触发在PWMMCR中配置的操作。当MR0和TC相等时，我们进行复位TC从新计数从而固定了PWM的周期频率。当定时器处于PWM模式时，软件对PWM匹配寄存器MR的写操作，写入值实际上被保存在一个映像寄存器中，不会被立即使用。所以在我们需要操作PWM锁存使能寄存器PWMLER，典型序列为：将新值写入MR，写PWMLER中相应的位，更改的MR值将在下一次定时器复位时生效。

        在下面的程序中，将给MR1中写入不同的匹配值，来控制PWM的占空比。为了方便使用LED灯进行示意。
[cpp] view plain copy print ?
1. #define CCLK 120000000
2. #define PCLK 60000000
4. #define rFIO1DIR (*(volatile unsigned*)(0x20098020))
5. #define rFIO1MASK (*(volatile unsigned*)(0x20098030))
6. #define rFIO1PIN (*(volatile unsigned*)(0x20098034))
7. #define rFIO1SET (*(volatile unsigned*)(0x20098038))
8. #define rFIO1CLR (*(volatile unsigned*)(0x2009803c))
10. #define rCLKSRCSEL (*(volatile unsigned *)(0x400FC10C)) //时钟源选择寄存器
11. #define rPLL0CON (*(volatile unsigned *)(0x400FC080)) //PLL0控制寄存器
12. #define rPLL0CFG (*(volatile unsigned *)(0x400FC084)) //PLL0配置寄存器
13. #define rPLL0STAT (*(volatile unsigned *)(0x400FC088)) //PLL0状态寄存器
14. #define rPLL0FEED (*(volatile unsigned *)(0x400FC08C)) //PLL0馈送寄存器
15. #define rPLL1CON (*(volatile unsigned *)(0x400FC0A0))
16. #define rPLL1CFG (*(volatile unsigned *)(0x400FC0A4))
17. #define rPLL1STAT (*(volatile unsigned *)(0x400FC0A8))
18. #define rPLL1FEED (*(volatile unsigned *)(0x400FC0AC))
19. #define rCCLKSEL (*(volatile unsigned *)(0x400FC104)) //CPU时钟选择寄存器
20. #define rUSBCLKSEL (*(volatile unsigned *)(0x400FC108)) //USB时钟选择寄存器
21. #define rPCLKSEL (*(volatile unsigned *)(0x400FC1A8)) //外设时钟寄存器
22. #define rPCON (*(volatile unsigned *)(0x400FC0C0))
23. #define rPXCONP (*(volatile unsigned *)(0x400FC0C4))
24. #define rSCS (*(volatile unsigned *)(0x400FC1A0)) //系统控制和状态寄存器
25. #define rCLKOUTCFG (*(volatile unsigned *)(0x400FC1C8))
27. #define rIOCON_P1_02 (*(volatile unsigned *)(0x4002C088))
28. #define rPCONP (*(volatile unsigned *)(0x400FC0C4))
30. #define rPWM0IR (*(volatile unsigned *)(0x40014000))
31. #define rPWM0TCR (*(volatile unsigned *)(0x40014004))
32. #define rPWM0TC (*(volatile unsigned *)(0x40014008))
33. #define rPWM0PR (*(volatile unsigned *)(0x4001400C))
34. #define rPWM0CTCR (*(volatile unsigned *)(0x40014070))
35. #define rPWM0MCR (*(volatile unsigned *)(0x40014014))
36. #define rPWM0MR0 (*(volatile unsigned *)(0x40014018))
37. #define rPWM0MR1 (*(volatile unsigned *)(0x4001401C))
38. #define rPWM0CCR (*(volatile unsigned *)(0x40014028))
39. #define rPWM0PCR (*(volatile unsigned *)(0x4001404C))
40. #define rPWM0LER (*(volatile unsigned *)(0x40014050))
42. #define rISER1 (*(volatile unsigned *)(0xE000E104))
43. #define rCER1 (*(volatile unsigned *)(0xE000E184))
45. unsigned int duty = 10;
46. unsigned char match_cnt = 0;
48. void PWM0_IRQHandler(void)
49. {
50. if(rPWM0IR&0x1)
51. {
52. rFIO1PIN |= (1<<18);
53. match_cnt++;
54. rPWM0IR |= 0x1; //MR0中断复位
55. }
57. if(rPWM0IR&(0x1<<1))
58. {
59. rFIO1PIN &= ~(1<<18);
60. rPWM0IR |= 0x1<<1; //MR1中断复位
61. }
62. }
64. void SystemInit()
65. {
66. rSCS &= ~(0x1<<4); //频率12M
67. rSCS |= (0x1<<5); //使能主振荡器
68. while(0 == (rSCS & (0x1<<6)));//等待主振荡器稳定
70. rCLKSRCSEL = 0x1;
72. rPLL0CFG = 0x9; //配置CCLK = 120M
73. rPLL0CON = 0x01;
74. rPLL0FEED = 0xAA;
75. rPLL0FEED =0x55;
76. while( 0 == (rPLL0STAT & (0x1<<10)));
78. rCCLKSEL = (0x1 | (0x1<<8));
79. rPCLKSEL = 0x2; //配置PCLK = 60M
81. rCLKOUTCFG = 0x0 | (0xb<<4) | (0x1<<8);
82. }
85. void PWMInit()
86. {
87. rIOCON_P1_02 &= ~0x7;
88. rIOCON_P1_02 |= 0x3; //P1.02配置成PWM0[1]
90. rPCONP |= 0x1<<5; //使能PWM0外设
92. rPWM0IR = 0x73F; //初始化PWM相关控制寄存器
93. rPWM0TCR = 0;
94. rPWM0CTCR = 0;
95. rPWM0MCR = 0;
96. rPWM0CCR = 0;
97. rPWM0PCR = 0;
98. rPWM0LER = 0;
100. rPWM0PR = 0x1<<20; //每0x1<<20+1个PLCK上升沿，TC递增
101. rPWM0TCR |= 0x1<<1; //复位TC和PC
102. rPWM0TCR &= ~(0x1<<1);
104. rPWM0MR0 = 100;
105. rPWM0LER |= 0x1;
106. rPWM0MCR |= 0x1<<1 | 0x1; //MR0和TC匹配时复位TC和PC.并且产生中断
108. rPWM0MR1 = duty;
109. rPWM0LER |= 0x1<<1;
110. rPWM0MCR |= 0x1<<3; //MR1和TC匹配时产生中断
111. }
113. int main ()
114. {
115. PWMInit();
117. rFIO1DIR |= (0x1<<18);
118. rISER1 |= 0x1<<7; //PWM0中断使能
120. rPWM0TCR |= 0x1<<1; //复位TC和PC
121. rPWM0TCR &= ~(0x1<<1);
123. rPWM0TCR |= 0x1; //PC和TC计数使能
124. rPWM0TCR |= 0x1<<3; //PWM模式使能
126. while(1)
127. {
128. if(match_cnt >= 1)
129. {
130. match_cnt = 0;
131. duty = duty+10;
132. if(duty >= 100)
133. {
134. duty = 0;
135. }
136. rPWM0MR1 = duty;
137. rPWM0LER |= 0x1<<1;
138. rPWM0MCR |= 0x1<<3;
139. }
140. }
141. return 1;
142. }
```
#define CCLK		120000000
#define PCLK		 60000000

#define rFIO1DIR	(*(volatile unsigned*)(0x20098020))
#define rFIO1MASK 	(*(volatile unsigned*)(0x20098030))
#define rFIO1PIN	(*(volatile unsigned*)(0x20098034))
#define rFIO1SET	(*(volatile unsigned*)(0x20098038))
#define rFIO1CLR	(*(volatile unsigned*)(0x2009803c))

#define rCLKSRCSEL  (*(volatile unsigned *)(0x400FC10C))     //时钟源选择寄存器  
#define rPLL0CON    (*(volatile unsigned *)(0x400FC080))     //PLL0控制寄存器  
#define rPLL0CFG    (*(volatile unsigned *)(0x400FC084))     //PLL0配置寄存器  
#define rPLL0STAT   (*(volatile unsigned *)(0x400FC088))     //PLL0状态寄存器  
#define rPLL0FEED   (*(volatile unsigned *)(0x400FC08C))     //PLL0馈送寄存器  
#define rPLL1CON    (*(volatile unsigned *)(0x400FC0A0))       
#define rPLL1CFG    (*(volatile unsigned *)(0x400FC0A4))  
#define rPLL1STAT   (*(volatile unsigned *)(0x400FC0A8))  
#define rPLL1FEED   (*(volatile unsigned *)(0x400FC0AC))  
#define rCCLKSEL    (*(volatile unsigned *)(0x400FC104))     //CPU时钟选择寄存器  
#define rUSBCLKSEL  (*(volatile unsigned *)(0x400FC108))     //USB时钟选择寄存器  
#define rPCLKSEL    (*(volatile unsigned *)(0x400FC1A8))     //外设时钟寄存器  
#define rPCON       (*(volatile unsigned *)(0x400FC0C0))  
#define rPXCONP     (*(volatile unsigned *)(0x400FC0C4))  
#define rSCS        (*(volatile unsigned *)(0x400FC1A0))     //系统控制和状态寄存器  
#define rCLKOUTCFG  (*(volatile unsigned *)(0x400FC1C8))

#define rIOCON_P1_02	(*(volatile unsigned *)(0x4002C088))
#define rPCONP		(*(volatile unsigned *)(0x400FC0C4))

#define rPWM0IR 	(*(volatile unsigned *)(0x40014000))
#define rPWM0TCR	(*(volatile unsigned *)(0x40014004))
#define rPWM0TC		(*(volatile unsigned *)(0x40014008))
#define rPWM0PR 	(*(volatile unsigned *)(0x4001400C))
#define rPWM0CTCR	(*(volatile unsigned *)(0x40014070))
#define rPWM0MCR	(*(volatile unsigned *)(0x40014014))
#define rPWM0MR0	(*(volatile unsigned *)(0x40014018))
#define rPWM0MR1	(*(volatile unsigned *)(0x4001401C))
#define rPWM0CCR	(*(volatile unsigned *)(0x40014028))
#define rPWM0PCR	(*(volatile unsigned *)(0x4001404C))
#define rPWM0LER	(*(volatile unsigned *)(0x40014050))

#define rISER1  	(*(volatile unsigned *)(0xE000E104))
#define rCER1		(*(volatile unsigned *)(0xE000E184))

unsigned int duty = 10;
unsigned char match_cnt = 0;

void PWM0_IRQHandler(void)
{
	if(rPWM0IR&0x1)
	{
		rFIO1PIN |= (1<<18);
		match_cnt++;
		rPWM0IR |= 0x1; 	//MR0中断复位
	}
	
	if(rPWM0IR&(0x1<<1))
	{
		rFIO1PIN &= ~(1<<18);
		rPWM0IR |= 0x1<<1;  //MR1中断复位
	}
}

void SystemInit()  
{  
    rSCS &= ~(0x1<<4);                //频率12M  
    rSCS |= (0x1<<5);             //使能主振荡器  
    while(0 == (rSCS & (0x1<<6)));//等待主振荡器稳定  
      
    rCLKSRCSEL = 0x1;  
      
    rPLL0CFG = 0x9;                 //配置CCLK = 120M  
    rPLL0CON = 0x01;  
    rPLL0FEED = 0xAA;  
    rPLL0FEED =0x55;  
    while( 0 == (rPLL0STAT & (0x1<<10)));   
      
    rCCLKSEL = (0x1 | (0x1<<8));  
    rPCLKSEL = 0x2;                 //配置PCLK = 60M  
      
    rCLKOUTCFG = 0x0 | (0xb<<4) | (0x1<<8);  
} 


void PWMInit()
{
	rIOCON_P1_02 &= ~0x7;
	rIOCON_P1_02 |= 0x3;	//P1.02配置成PWM0[1]
	
	rPCONP |= 0x1<<5; 	//使能PWM0外设
	
	rPWM0IR = 0x73F;	//初始化PWM相关控制寄存器
	rPWM0TCR = 0;
	rPWM0CTCR = 0;
	rPWM0MCR = 0;
	rPWM0CCR = 0;
	rPWM0PCR = 0;
	rPWM0LER = 0;
	
	rPWM0PR = 0x1<<20;	//每0x1<<20+1个PLCK上升沿，TC递增
	rPWM0TCR |= 0x1<<1; 	//复位TC和PC
	rPWM0TCR &= ~(0x1<<1);
	
	rPWM0MR0 = 100;
	rPWM0LER |= 0x1;
	rPWM0MCR |= 0x1<<1 | 0x1; 	//MR0和TC匹配时复位TC和PC.并且产生中断
	
	rPWM0MR1 = duty;
	rPWM0LER |= 0x1<<1;
	rPWM0MCR |= 0x1<<3; 	//MR1和TC匹配时产生中断
}

int main ()
{
	PWMInit();
	
	rFIO1DIR |= (0x1<<18);
	rISER1 |= 0x1<<7;	//PWM0中断使能
	
	rPWM0TCR |= 0x1<<1; 	//复位TC和PC
	rPWM0TCR &= ~(0x1<<1);
	
	rPWM0TCR |= 0x1;	//PC和TC计数使能
	rPWM0TCR |= 0x1<<3; //PWM模式使能
	
	while(1)
	{
		if(match_cnt >= 1)
		{
			match_cnt = 0;
			duty = duty+10;
			if(duty >= 100)
			{
				duty  = 0;
			}
			rPWM0MR1 = duty;
			rPWM0LER |= 0x1<<1;
			rPWM0MCR |= 0x1<<3;
		}
	}
	return 1;
}
```
程序在MR0匹配时复位TC，在MR1匹配时触发边沿。可以看到随着MR1匹配值的改变，LED灯的亮灭时间对应改变。（程序中的预分频寄存器PR设置为了让LED效果明显）

LPC1788的PWM可以进行双边沿的控制。如PWM0.2可以用MR0控制PWM的周期频率，用MR1和MR2控制PWM0.2的边沿。
作者：tdyizhen1314（一位从事软硬件开发十年以上的老兵的故事，希望与大家一起交流，共同进步）邮箱：495567686@qq.com
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原文地址：https://www.cnblogs.com/tdyizhen1314/p/2704589.html