系统时钟和定时器——PWM定时器

E) /*判断是否重启*/

{

rTCON &= ~0x1F;

rTCON |= 0xf;

rTCON &= ~0x2 ; /*恢复PWM功能*/

}

}

/*4个LED随着频率的高低，时灭时亮。灯亮的数目4-3-2-1*/

if(freq == 100)

rGPBDAT = ~0x560; /*0001 1110 0000 取反之后1110 0001 1111*/

if(freq == 1300)

rGPBDAT = ~0x160; /*1110 0000取反之后 0001 1111*/

if(freq == 2500)

rGPBDAT = ~0x60; /*0110 0000取反之后 1001 1111*/

if(freq == 3700)

rGPBDAT = ~0x20; /*0010 0000取反之后 1101 1111*/

if(freq == 4900)

rGPBDAT = ~0x0; /*0000取反之后 1111111111*/

}

/*频率递减*/

for( ; freq>50 ; )

{

freq-=10;

rTCMPB0 = freq;

delay(20000);

while (stop == TRUE)

{

delay(1000);

if (stop ==FALSE)

{

rTCON &= ~0x1F;

rTCON |= 0xf;

rTCON &= ~0x2 ;

}

}

if(freq == 100)

rGPBDAT = ~0x560;

if(freq == 1300)

rGPBDAT = ~0x160;

if(freq == 2500)

rGPBDAT = ~0x60;

if(freq == 3700)

rGPBDAT = ~0x20;

if(freq == 4900)

rGPBDAT = ~0x0;

}

}

}

TOUT输出的波形是：

上图是频率上升时的大致波形图。由此可以看出高电平在每个周期中维持的时间越来越长，低电平时间越来越短。频率下降时的波形图正好相反。