定时器和WDT

1、概述

MSP430F149有三个时钟源：外部LF（XT1一般为32.768K）,HF(XT2一般为8M),内部DCO。从时钟系统模块可得到三种时钟信号：MCLK,SMCLK,ACLK。

上电默认状况下MCLK,SMCLK信号来自DCO，ACLK来自LF。根据官方PDF说法默认状况下DCO模块配置为RSELX=4，DCO=3，因此DCO应为1M,但示波器实测MCLK/SMCLK为680K，测试温度约25摄氏度。

标注：MCLK主时钟、SMCLK子时钟、ACLK活动时钟。

P5.4，P5.5，P5.6的第二功能分别对应MCLK,SMCLK,ACLK时钟信号，可用示波器测量。测试时发现频率后两位一直在跳动，频率稳定度很差。

MSP430系列单片机选择晶振为时钟源时，时钟周期就是晶振周期。一个机器周期＝一个时钟周期，即430每个动作都能完成一个基本操作；一个指令周期＝1～6个机器周期，具体根据具体指令而定。如果选择8M晶振，则一个机器周期为125ns。51单片机选择12M晶振，它的机器周期是时钟周期/12，一个机器周期为1us,可见MSP430的的速度是51的8倍。

2、使用方法概述

2.1 程序架构

一般在系统初始化关闭看门狗后要配置系统时钟，配置步骤为:

1、打开晶振；

2、等待晶振起振。清除OFIFG，延时，判断OFIFG是否为0，为0则晶振正常起振，退出判断；

3、选择MCLK/SMCLK时钟源；

uchar iq0;

BCSCTL1&=~XT2OFF; //打开XT2振荡器

do

{

IFG1 &= ~OFIFG; // 清除振荡器失效标志

for (iq0 = 0xFF; iq0 > 0; iq0--); // 延时，等待XT2起振

}

while ((IFG1 & OFIFG) != 0); // 判断XT2是否起振

BCSCTL2 =SELM_2+SELS; //选择MCLK、SMCLK为XT2

2.2 细节描述

对于DCO可以通过配置电阻和DCO得到不同的频率。电阻可配置片内或片外（DCOR一般片内）,片内电阻有8中选择（RSELX）,DCO有8中选择（DCOX）。

3、相关寄存器

1、DCOCTL

DCOx Bits

7-5

DCO frequency select. These bits select which of the eight discrete DCO

frequencies of the RSELx setting is selected.

2、BCSCTL0

XT2OFF Bit 7 XT2 off. This bit turns off the XT2 oscillator

0 XT2 is on

1 XT

2 is off if it is not used for MCLK or SMCLK.

RSELx Bits

2-0

Resistor Select. The internal resistor is selected in eight different steps.

The value of the resistor defines the nominal frequency. The lowest

nominal frequency is selected by setting RSELx=0.

3、BCSCTL0

SELMx Bits

7-6

Select MCLK. These bits select the MCLK source.

00 DCOCLK

01 DCOCLK

10 XT2CLK when XT2 oscillator present on-chip. LFXT1CLK when XT2

oscillator not present on-chip.

11 LFXT1CLK

SELS Bit 3 Select SMCLK. This bit selects the SMCLK source.

0 DCOCLK

1 XT2CLK when XT

2 oscillator present on-chip. LFXT1CLK when XT2

oscillator not present on-chip.

DCOR Bit 0 DCO resistor select

0 Internal resistor

1 External resistor

4、实例

4.1 配置MCLK/SMCLK

见本节2.1。

4.2配置DCO

void main(void)

{

WDTCTL = WDTPW +WDTHOLD; // Stop Watchdog Timer

DCOCTL = DCO0 + DCO1 + DCO2; // Max DCO BCSCTL1 = RSEL0 + RSEL1 + RSEL2; // XT2on, max RSEL BCSCTL2 |= SELS; // SMCLK = XT2

P5DIR |= 0x70; // P5.6,5,4 outputs P5SEL |= 0x70; // P5.6,5,5 options while(1)

{

}

}

实测DCO最低128K，最高4.58M。

1、概述

看门狗有两个作用：1、可以防止程序跑飞，若程序跑飞可让单片机复位；2、可作为间隔时间发生器，在中断中进行定期刷新显示、读取数据等对外设的操作。

2、设置

不需要看门狗时可用软件关闭，设置：WDTCTL = WDTPW + WDTHOLD;

为防止误触发操作WDTCTL需要先写入WDTPW。

作为间隔定时器时详细操作可见MSP430F149.H文件中的宏定义。

3、相关寄存器

1、WDTCTL Watchdog Timer Register

WDTPW Bits

15-8

Watchdog timer password. Always read as 069h. Must be written as 05Ah, or

a PUC will be generated.

WDTHOLD Bit 7 Watchdog timer hold. This bit stops the watchdog timer. Setting WDTHOLD= 1 when the WDT is not in use conserves power.

0 Watchdog timer is not stopped

1 Watchdog timer is stopped

WDTTMSEL Bit 4 Watchdog timer mode select

0 Watchdog mode

1 Interval timer mode

WDTCNTCL Bit 3 Watchdog timer counter clear. Setting WDTCNTCL = 1 clears the count value to 0000h. WDTCNTCL is automatically reset.

0 No action

1 WDTCNT = 0000h

2、IE1 Interrupt Enable Register 1

WDTIE Bit 0 Watchdog timer interrupt enable. This bit enables the WDTIFG interrupt for interval timer mode. It is not necessary to set this bit for watchdog mode.

Because other bits in IE1 may be used for other modules, it is recommended

to set or clear this bit using BIS.B or BIC.B instructions, rather than MOV.B

or CLR.B instructions.

0 Interrupt not enabled

1 Interrupt enabled

4、设计实例

4.1 利用WDT定时模式在中断函数中定时操作外设

说明：#define WDT_MDLY_32 (WDTPW+WDTTMSEL+WDTCNTCL)

void main(void)

{

WDTCTL = WDT_MDLY_32; // Set Watchdog Timer interval to ~30ms IE1 |= WDTIE; // Enable WDT interrupt

P2DIR |= 0x01; // Set P1.0 to output direction

_BIS_SR(LPM0_bits + GIE); // Enter LPM0 w/ interrupt

}

// Watchdog Timer interrupt service routine

#pragma vector=WDT_VECTOR

__interrupt void watchdog_timer(void)

{

P2OUT ^= 0x01; // Toggle P1.0 using exclusive-OR }

4.2 利用WDT定时模式延时

WDTCTL = WDT_ADLY_1000;//延时1000ms

//延时2s

for(i = 0; i < 3; i++)

{

IFG1 &= ~WDTIFG;

while(!(IFG1 & WDTIFG));

}

IFG1 &= ~WDTIFG;

#include

typedef unsigned char uchar;

uchar step = 0xff;

void main( void )

{

uchar i;

WDTCTL = WDTPW + WDTHOLD; //关狗

P1DIR = 0XFF;P1OUT = 0XFF; //关闭所有I/O口

P2DIR = 0XFF;P2OUT = 0XFF;

P3DIR = 0XFF;P3OUT = 0XFF;

P4DIR = 0XFF;P4OUT = 0XFF;

P5DIR = 0XFF;P5OUT = 0XFF;

P6DIR = 0XFF;P6OUT = 0XFF;

BCSCTL1 &= ~XT2OFF; //打开XT2高频晶体振荡器

do

{

IFG1 &= ~OFIFG; //清除晶振失败标志

for (i = 0xFF; i > 0; i--); //等待8MHz晶体起振

}

while ((IFG1 & OFIFG)); //晶振失效标志仍然存在？

BCSCTL2 |= SELM_2 + SELS; //MCLK和SMCLK选择高频晶振

TACCTL0 |= CCIE; //使能比较中断

TACTL |= TASSEL_2 + ID_3 ; //计数时钟选择SMLK=8MHz，1/8分频后为1MHz

TBCCR0 = 4096*2 - 1; //周期两秒

TBCCTL0 |= CCIE;

TBCTL |= TBSSEL_1 + ID_3 + MC_1; //时钟源ACLK/8，up mode

P6DIR |= BIT7; //蜂鸣器对应IO设置为输出

P2DIR = 0xff;

P2OUT = 0xff;

_EINT();

LPM1;

}

#pragma vector=TIMERA0_VECTOR

__interrupt void Timer_A (void)

{

P6OUT ^= BIT7; // Toggle P6.7

}

#pragma vector=TIMERB0_VECTOR

__interrupt void Timer_B (void)

{

if(step == 0xff) //up mode

TACTL |= MC_1;

step++;

switch(step)

{

case 0: TACCR0 = 5000; P2OUT = ~1; break; // 100Hz case 1: TACCR0 = 2500; P2OUT = ~2; break; // 200Hz case 2: TACCR0 = 1250; P2OUT = ~3; break; // 400Hz case 3: TACCR0 = 625; P2OUT = ~4; break; // 800Hz case 4: TACCR0 = 500; P2OUT = ~5; break; // 1KHz case 5: TACCR0 = 250; P2OUT = ~6; break; // 2KHz case 6: TACCR0 = 167; P2OUT = ~7; break; // 3KHz case 7: TACCR0 = 125; P2OUT = ~8; break; // 4KHz case 8: TACCR0 = 100; P2OUT = ~9; break; // 5KHz case 9: TACCR0 = 83; P2OUT = ~10; break; // 6KHz case 10: TACCR0 = 71; P2OUT = ~11; break; // 7KHz case 11: TACCR0 = 63; P2OUT = ~12; break; // 8KHz case 12: TACCR0 = 56; P2OUT = ~13; break; // 9KHz case 13: TACCR0 = 50; P2OUT = ~14; break; // 10KHz case 14: TACCR0 = 33; P2OUT = ~15; break; // 15KHz case 15: TACCR0 = 25; P2OUT = ~16; break; // 20KHz case 16: step = 0xff; // 循环播放

}

}