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51单片机超声波测距程序为什么RX=1时开启计时器，RX=0时关闭计时器程序如下。

aecs6 • 2023-5-5 • CMS教程 • 阅读 33

51单片机超声波测距程序为什么RX=1时开启计时器，RX=0时关闭计时器程序如下。,第1张

RX是串口接收完成标志位。当串口接收到完整的数据帧时RX由硬置1。用户需要手动清0，以接收下一字节。

while(1)

{

while(!RX);//等待串口接收1字节数据

TR0=1;//启动计数

while(RX);//等待清0，初步判断是在定时器0中清RX。

TR0=0;//结束计数

conut();

}

这是一个超声波避障小车的源程序，可以参考下，用的89C52单片机，舵机控制转角避障。

#include<AT89x51H>

#include <intrinsh>

#define Sevro_moto_pwm P2_7 //接舵机信号端输入PWM信号调节速度

#define ECHO P2_4 //超声波接口定义

#define TRIG P2_5 //超声波接口定义

#define Left_moto_go {P1_0=1,P1_1=0,P1_2=1,P1_3=0;} //左边两个电机向前走

#define Left_moto_back {P1_0=0,P1_1=1,P1_2=0,P1_3=1;} //左边两个电机向后转

#define Left_moto_Stop {P1_0=0,P1_1=0,P1_2=0,P1_3=0;} //左边两个电机停转

#define Right_moto_go {P1_4=1,P1_5=0,P1_6=1,P1_7=0;} //右边两个电机向前走

#define Right_moto_back {P1_4=0,P1_5=1,P1_6=0,P1_7=1;} //右边两个电机向前走

#define Right_moto_Stop {P1_4=0,P1_5=0,P1_6=0,P1_7=0;} //右边两个电机停转

unsigned char const discode[] ={ 0xC0,0xF9,0xA4,0xB0,0x99,0x92,0x82,0xF8,0x80,0x90,0xBF,0xff/-/};

unsigned char const positon[3]={ 0xfe,0xfd,0xfb};

unsigned char disbuff[4] ={ 0,0,0,0,};

unsigned char posit=0;

unsigned char pwm_val_left = 0;//变量定义

unsigned char push_val_left =14;//舵机归中，产生约，15MS 信号

unsigned long S=0;

unsigned long S1=0;

unsigned long S2=0;

unsigned long S3=0;

unsigned long S4=0;

unsigned int time=0; //时间变量

unsigned int timer=0; //延时基准变量

unsigned char timer1=0; //扫描时间变量

//

void delay(unsigned int k) //延时函数

{

unsigned int x,y;

for(x=0;x<k;x++)

for(y=0;y<2000;y++);

}

//

void Display(void) //扫描数码管

{

if(posit==0)

{P0=(discode[disbuff[posit]])&0x7f;}//产生点

else

{P0=discode[disbuff[posit]];} if(posit==0)

{ P2_1=0;P2_2=1;P2_3=1;}

if(posit==1)

{P2_1=1;P2_2=0;P2_3=1;}

if(posit==2)

{P2_1=1;P2_2=1;P2_3=0;}

if(++posit>=3)

posit=0;

}

//

void StartModule() //启动测距信号

{

TRIG=1;

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

_nop_();

TRIG=0;

}

//

void Conut(void) //计算距离

{

while(!ECHO); //当RX为零时等待

TR0=1; //开启计数

while(ECHO); //当RX为1计数并等待

TR0=0; //关闭计数

time=TH0256+TL0; //读取脉宽长度

TH0=0;

TL0=0;

S=(time17)/100; //算出来是CM

disbuff[0]=S%1000/100; //更新显示

disbuff[1]=S%1000%100/10;

disbuff[2]=S%1000%10 %10;

}

//

//前速前进

void run(void)

{

Left_moto_go ; //左电机往前走

Right_moto_go ; //右电机往前走

}

//

//前速后退

void backrun(void)

{

Left_moto_back ; //左电机往前走

Right_moto_back ; //右电机往前走

}

//

//左转

void leftrun(void)

{

Left_moto_back ; //左电机往前走

Right_moto_go ; //右电机往前走

}

//

//右转

void rightrun(void)

{

Left_moto_go ; //左电机往前走

Right_moto_back ; //右电机往前走

}

//

//STOP

void stoprun(void)

{

Left_moto_Stop ; //左电机停走

Right_moto_Stop ; //右电机停走

}

//

void COMM( void )

{

push_val_left=5; //舵机向左转90度

timer=0;

while(timer<=4000); //延时400MS让舵机转到其位置

StartModule(); //启动超声波测距

Conut(); //计算距离

S2=S;

push_val_left=23; //舵机向右转90度

timer=0;

while(timer<=4000); //延时400MS让舵机转到其位置

StartModule(); //启动超声波测距

Conut(); //计算距离

S4=S;

push_val_left=14; //舵机归中

timer=0;

while(timer<=4000); //延时400MS让舵机转到其位置 StartModule(); //启动超声波测距

Conut(); //计算距离

S1=S; if((S2<20)||(S4<20)) //只要左右各有距离小于20CM小车后退

{

backrun(); //后退

timer=0;

while(timer<=4000);

}

if(S2>S4)

{

rightrun(); //车的左边比车的右边距离小 右转

timer=0;

while(timer<=4000);

}

else

{

leftrun(); //车的左边比车的右边距离大 左转

timer=0;

while(timer<=4000);

}

} //

/ PWM调制电机转速 /

//

/ 左电机调速 /

/调节push_val_left的值改变电机转速,占空比 /

void pwm_Servomoto(void)

{

if(pwm_val_left<=push_val_left)

Sevro_moto_pwm=1;

else

Sevro_moto_pwm=0;

if(pwm_val_left>=200)

pwm_val_left=0;

}

//

///TIMER1中断服务子函数产生PWM信号/

void time1()interrupt 3 using 2

{

TH1=(65536-100)/256; //100US定时

TL1=(65536-100)%256;

timer++; //定时器100US为准。在这个基础上延时

pwm_val_left++;

pwm_Servomoto(); timer1++; //2MS扫一次数码管

if(timer1>=20)

{

timer1=0;

Display();

}

}

//

///TIMER0中断服务子函数产生PWM信号/

void timer0()interrupt 1 using 0

{

} // void main(void)

{ TMOD=0X11;

TH1=(65536-100)/256; //100US定时

TL1=(65536-100)%256;

TH0=0;

TL0=0;

TR1= 1;

ET1= 1;

ET0= 1;

EA = 1; delay(100);

push_val_left=14; //舵机归中

while(1) /无限循环/

{ if(timer>=1000) //100MS检测启动检测一次

{

timer=0;

StartModule(); //启动检测

Conut(); //计算距离

if(S<30) //距离小于20CM

{

stoprun(); //小车停止

COMM(); //方向函数

}

else

if(S>30) //距离大于，30CM往前走

run();

}

}

}

//

下面是头文件：

头文件（一）

/--------------------------------------------------------------------------

AT89X51H Header file for the low voltage Flash Atmel AT89C51 and AT89LV51

Copyright (c) 1988-2002 Keil Elektronik GmbH and Keil Software, Inc

All rights reserved

--------------------------------------------------------------------------/

#ifndef __AT89X51_H__

#define __AT89X51_H__

/------------------------------------------------

Byte Registers

------------------------------------------------/

sfr P0 = 0x80;

sfr SP = 0x81;

sfr DPL = 0x82;

sfr DPH = 0x83;

sfr PCON = 0x87;

sfr TCON = 0x88;

sfr TMOD = 0x89;

sfr TL0 = 0x8A;

sfr TL1 = 0x8B;

sfr TH0 = 0x8C;

sfr TH1 = 0x8D;

sfr P1 = 0x90;

sfr SCON = 0x98;

sfr SBUF = 0x99;

sfr P2 = 0xA0;

sfr IE = 0xA8;

sfr P3 = 0xB0;

sfr IP = 0xB8;

sfr PSW = 0xD0;

sfr ACC = 0xE0;

sfr B = 0xF0;

/------------------------------------------------

P0 Bit Registers

------------------------------------------------/

sbit P0_0 = 0x80;

sbit P0_1 = 0x81;

sbit P0_2 = 0x82;

sbit P0_3 = 0x83;

sbit P0_4 = 0x84;

sbit P0_5 = 0x85;

sbit P0_6 = 0x86;

sbit P0_7 = 0x87;

/------------------------------------------------

PCON Bit Values

------------------------------------------------/

#define IDL_ 0x01

#define STOP_ 0x02

#define PD_ 0x02 / Alternate definition /

#define GF0_ 0x04

#define GF1_ 0x08 #define SMOD_ 0x80 /

------------------------------------------------

TCON Bit Registers

------------------------------------------------/

sbit IT0 = 0x88;

sbit IE0 = 0x89;

sbit IT1 = 0x8A;

sbit IE1 = 0x8B;

sbit TR0 = 0x8C;

sbit TF0 = 0x8D;

sbit TR1 = 0x8E;

sbit TF1 = 0x8F;

/------------------------------------------------

TMOD Bit Values

------------------------------------------------/

#define T0_M0_ 0x01

#define T0_M1_ 0x02

#define T0_CT_ 0x04

#define T0_GATE_ 0x08

#define T1_M0_ 0x10

#define T1_M1_ 0x20

#define T1_CT_ 0x40

#define T1_GATE_ 0x80

#define T1_MASK_ 0xF0

#define T0_MASK_ 0x0F

/------------------------------------------------

P1 Bit Registers

------------------------------------------------/

sbit P1_0 = 0x90;

sbit P1_1 = 0x91;

sbit P1_2 = 0x92;

sbit P1_3 = 0x93;

sbit P1_4 = 0x94;

sbit P1_5 = 0x95;

sbit P1_6 = 0x96;

sbit P1_7 = 0x97; /

------------------------------------------------

SCON Bit Registers

------------------------------------------------/

sbit RI = 0x98;

sbit TI = 0x99;

sbit RB8 = 0x9A;

sbit TB8 = 0x9B;

sbit REN = 0x9C;

sbit SM2 = 0x9D;

sbit SM1 = 0x9E;

sbit SM0 = 0x9F;

/------------------------------------------------

P2 Bit Registers

------------------------------------------------/

sbit P2_0 = 0xA0;

sbit P2_1 = 0xA1;

sbit P2_2 = 0xA2;

sbit P2_3 = 0xA3;

sbit P2_4 = 0xA4;

sbit P2_5 = 0xA5;

sbit P2_6 = 0xA6;

sbit P2_7 = 0xA7;

/------------------------------------------------

IE Bit Registers

------------------------------------------------/

sbit EX0 = 0xA8; / 1=Enable External interrupt 0 /

sbit ET0 = 0xA9; / 1=Enable Timer 0 interrupt /

sbit EX1 = 0xAA; / 1=Enable External interrupt 1 /

sbit ET1 = 0xAB; / 1=Enable Timer 1 interrupt /

sbit ES = 0xAC; / 1=Enable Serial port interrupt /

sbit ET2 = 0xAD; / 1=Enable Timer 2 interrupt / sbit EA = 0xAF; / 0=Disable all interrupts /

/------------------------------------------------

P3 Bit Registers (Mnemonics & Ports)

------------------------------------------------/

sbit P3_0 = 0xB0;

sbit P3_1 = 0xB1;

sbit P3_2 = 0xB2;

sbit P3_3 = 0xB3;

sbit P3_4 = 0xB4;

sbit P3_5 = 0xB5;

sbit P3_6 = 0xB6;

sbit P3_7 = 0xB7; sbit RXD = 0xB0; / Serial data input /

sbit TXD = 0xB1; / Serial data output /

sbit INT0 = 0xB2; / External interrupt 0 /

sbit INT1 = 0xB3; / External interrupt 1 /

sbit T0 = 0xB4; / Timer 0 external input /

sbit T1 = 0xB5; / Timer 1 external input /

sbit WR = 0xB6; / External data memory write strobe /

sbit RD = 0xB7; / External data memory read strobe /

/------------------------------------------------

IP Bit Registers

------------------------------------------------/

sbit PX0 = 0xB8;

sbit PT0 = 0xB9;

sbit PX1 = 0xBA;

sbit PT1 = 0xBB;

sbit PS = 0xBC;

sbit PT2 = 0xBD;

/------------------------------------------------

PSW Bit Registers

------------------------------------------------/

sbit P = 0xD0;

sbit FL = 0xD1;

sbit OV = 0xD2;

sbit RS0 = 0xD3;

sbit RS1 = 0xD4;

sbit F0 = 0xD5;

sbit AC = 0xD6;

sbit CY = 0xD7;

/------------------------------------------------

Interrupt Vectors:

Interrupt Address = (Number 8) + 3

------------------------------------------------/

#define IE0_VECTOR 0 / 0x03 External Interrupt 0 /

#define TF0_VECTOR 1 / 0x0B Timer 0 /

#define IE1_VECTOR 2 / 0x13 External Interrupt 1 /

#define TF1_VECTOR 3 / 0x1B Timer 1 /

#define SIO_VECTOR 4 / 0x23 Serial port / #endif

头文件（二）

/--------------------------------------------------------------------------

INTRINSH Intrinsic functions for C51

Copyright (c) 1988-2002 Keil Elektronik GmbH and Keil Software, Inc

All rights reserved

--------------------------------------------------------------------------/

#ifndef __INTRINS_H__

#define __INTRINS_H__ extern void _nop_ (void);

extern bit _testbit_ (bit);

extern unsigned char _cror_ (unsigned char, unsigned char);

extern unsigned int _iror_ (unsigned int, unsigned char);

extern unsigned long _lror_ (unsigned long, unsigned char);

extern unsigned char _crol_ (unsigned char, unsigned char);

extern unsigned int _irol_ (unsigned int, unsigned char);

extern unsigned long _lrol_ (unsigned long, unsigned char);

extern unsigned char _chkfloat_(float); #endif

//超声波模块程序

//Trig = P2^0

//Echo = P3^2

#include <reg52h>

#define uchar unsigned char

#define uint unsigned int

//

void delay(uint z)

{

uint x,y;

for(x=z;x>0;x--)

for(y=110;y>0;y--);

}

//

void delay_20us()

{

uchar a ;

for(a=0;a<100;a++);

}

//

//显示数据转换程序

void display(uint temp)

{

uchar ge,shi,bai;

bai=temp/100;

shi=(temp%100)/10;

ge=temp%10;

wela=1;

P0=0xf7;

wela=0;

dula=1;

P0=table[bai];

dula=0;

delay(1);

dula=1;

P0=0x00; //关位码

dula=0;

wela=1;

P0=0xef;

wela=0;

dula=1;

P0=table[shi];

dula=0;

delay(1);

dula=1;

P0=0x00; //关位码

dula=0;

dula=1;

P0=table[ge];

dula=0;

wela=1;

P0=0xdf;

wela=0;

delay(1);

dula=1;

P0=0x00; //关位码

dula=0;

}

//

void main()

{

uint distance;

test =0;

Trig=0; //首先拉低脉冲输入引脚

EA=1; //打开总中断0

TMOD=0x10; //定时器1，16位工作方式

while(1)

{

EA=0; //关总中断

Trig=1; //超声波输入端

delay_20us(); //延时20us

Trig=0; //产生一个20us的脉冲

while(Echo==0); //等待Echo回波引脚变高电平

succeed_flag=0; //清测量成功标志

EA=1;

EX0=1; //打开外部中断0

TH1=0; //定时器1清零

TL1=0; //定时器1清零

TF1=0; //计数溢出标志

TR1=1; //启动定时器1

delay(20); //等待测量的结果

TR1=0; //关闭定时器1

EX0=0; //关闭外部中断0

if(succeed_flag==1)

{

time=timeH256+timeL;

distance=time0172; //厘米

display(distance);

}

if(succeed_flag==0)

{

distance=0; //没有回波则清零

test = !test; //测试灯变化

}

}

}

//

//外部中断0，用做判断回波电平

void exter() interrupt 0 // 外部中断0是0号

{

timeH =TH1; //取出定时器的值

timeL =TL1; //取出定时器的值

succeed_flag=1;//至成功测量的标志

EX0=0; //关闭外部中断

}

//

//定时器1中断,用做超声波测距计时

void timer1() interrupt 3 //

{

TH1=0;

TL1=0;

}

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