电路如图所示：

    M1是一个从旧的磁盘驱动器上拆下来的。它有5个引脚：公共端，线圈1，2，3和4.公

共端与各组线圈之间的电阻阻值很精确，均为75欧。那么当电压为＋5V时，每组线圈的驱

动电流为60mA。ULN2003是一个达灵顿管阵列，用来扩展2051的驱动能力。当电压为50V时

最大可提供500mA的电流。从电路图上可看到，2051的四个输出端P1.4到P1.7连接到了ULN

2003的输入端。四个4.7K的电阻帮助2051从电源处获得更多的驱动电流。串口可随意选择.

程序

stepper.c 

stepper.hex 

/* 

 * STEPPER.C 

 * sweeping stepper's rotor cw and cww 400 steps 

 * Copyright (c) 1999 by W.Sirichote 

 */ 

#include c:\mc51\8051io.h  /* include i/o header file */ 

#include c:\mc51\8051reg.h 

register unsigned char j,flag1,temp; 

register unsigned int cw_n,ccw_n; 

unsigned char step[8]={0x80,0xc0,0x40,0x60,0x20,0x30,0x10,0x90} 

#define n 400 

/* flag1 mask byte 

   0x01  run cw() 

   0x02  run ccw() 

*/ 

main() 

{ 

  flag1=0; 

  serinit(9600); 

  disable();  /* no need timer interrupt */ 

  cw_n = n;    /* initial step number for cw */ 

  flag1 |=0x01; /* initial enable cw() */ 

 while(1){ 

  { 

    tick_wait();  /* wait for 10ms elapsed */ 

    energize();   /* round-robin execution the following tasks every 10ms */ 

    cw(); 

    ccw(); 

  } 

        } 

} 

cw(){ 

       if((flag1&0x01)!=0) 

       { 

        cw_n--;       /* decrement cw step number */ 

        if (cw_n !=0) 

         j++;         /* if not zero increment index j */ 

         else 

         {flag1&=~0x01; /* disable cw() execution */ 

          ccw_n = n;    /* reload step number to ccw counter */ 

          flag1 |=0x02; /* enable cww() execution */ 

          } 

       } 

} 

ccw(){ 

       if((flag1&0x02)!=0) 

       { 

        ccw_n--;       /* decremnent ccw step number */ 

        if (ccw_n !=0) 

         j--;          /* if not zero decrement index j */ 

         else 

         {flag1&=~0x02; /* disable ccw() execution */ 

          cw_n = n;     /* reload step number to cw counter */ 

          flag1 |=0x01; /* enable cw() execution */ 

          } 

       } 

} 

tick_wait(){   /* cputick was replaced by simpler ASM code 10ms wait */ 

    asm" JNB TCON.5,*";   /* wait for TF0 set */ 

    asm" CLR TCON.5";     /* clear TF0 for further set */ 

    asm" ORL TH0,#$DC";   /* reload TH0 with $DC, TL0 = 0 */ 

} 

energize(){ 

    P1 = step[(j&0x07)];  /* only step 0-7 needed */ 

}

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