// Chapter 15 6811 C programs// Jonathan W. Valvano// This software accompanies the book,// Embedded Microcomputer Systems: Real Time Interfacing// published by Brooks Cole, 1999//  Program 15.1. Real time data acquisition with a simple digital filter, Equation 2.// MC68HC11A8#define Rate 2000#define OC5  0x08 #pragma interrupt_handler TOC5handler()void TOC5handler(void){   TFLG1=OC5;      // Ack interrupt    TOC5=TOC5+Rate; // Executed every 1 ms   x[1]=x[0];      // shift MACQ data   x[0] = A2D(channel);  // new data   y=(x[0]+x[1])>>1;}     void ritual(void) { asm(" sei");    // make atomic   TMSK1|=OC5;  // Arm output compare 5   x[0] = x[1] = 0;   TFLG1=OC5;  // Initially clear OC5F   TOC5=TCNT+Rate; // First one in 1 msasm(" cli"); }//  Program 15.2. Real time data acquisition with a simple digital filter, Equation 3.// MC68HC11A8#define OC5  0x08 #pragma interrupt_handler TOC5handler()void TOC5handler(void){ unsigned int i;   TFLG1=OC5;      // Ack interrupt    TOC5=TOC5+5556;    // fs=360Hz   for(i=5;i>0;i++)        x[i]=x[i-1];    // shift MACQ data   x[0] = A2D(channel);  // new data   y=(x[0]+x[1]+x[2]+x[3]+x[4]+x[5])/6;}     void ritual(void) { asm(" sei");    // make atomic   TMSK1|=OC5;  // Arm output compare 5   x[0]=x[1]=x[2]=x[3]=x[4]=x[5]=0;   TFLG1=OC5;  // Initially clear OC5F   TOC5=TCNT+5556; asm(" cli"); }//  Program 15.3. Real time data acquisition with a simple digital filter, Equation 4.// MC68HC11A8#define OC5  0x08 #pragma interrupt_handler TOC5handler()void TOC5handler(void){    TFLG1=OC5;      // Ack interrupt    TOC5=TOC5+5556;  // fs=360Hz   x[3]=x[2];       // shift MACQ data   x[2]=x[1];   x[1]=x[0];    x[0] = A2D(channel);  // new data   y=(x[0]+x[3])>>1;}     void ritual(void) { asm(" sei");    // make atomic   TMSK1|=OC5;  // Arm output compare 5   x[0]=x[1]=x[2]=x[3]=0;   TFLG1=OC5;  // Initially clear OC5F   TOC5=TCNT+5556; asm(" cli"); } // Program 15.4. Compiler listings for the filter implementation.; MC68HC11A8, ICC11; y=(x[0]+x[3])>>1;   ldy #1   pshy   ldab  _x+3  ; 8-bit x[3]   clra        ; promote into RegD   pshb        ; save on stack   psha   ldab  _x    ; 8 bit x[0]   clra        ; promote into RegD   tsy   addd 0,y    ; 16-bit x[0]+x[3]   puly   puly   jsr  __asrd ; 16-bit shift   stab  _y    ; demote to 8 bit//   Program 15.5. Real time data acquisition with a simple digital filter, Equation 5.// MC68HC11A8#define Rate 2000#define OC5  0x08 #pragma interrupt_handler TOC5handler()void TOC5handler(void){   TFLG1=OC5;      // Ack interrupt    TOC5=TOC5+Rate; // Executed at fs   y[1]=y[0];      // shift MACQ data   x = A2D(channel);  // new data   y[0]=(x+y[1])>>1;} // 16-bit  void ritual(void) { asm(" sei");    // make atomic   TMSK1|=OC5;  // Arm output compare 5   y[0] = y[1] = 0;   TFLG1=OC5;  // Initially clear OC5F   TOC5=TCNT+Rate; // First one in 1 msasm(" cli"); }// Program 15.6: The median filter is an example of a nonlinear filter.unsigned char Median(unsigned char u1,unsigned char u2,unsigned char u3){ unsigned char result;  if(u1>u2)    if(u2>u3)   result=u2;     // u1>u2,u2>u3       u1>u2>u3      else        if(u1>u3) result=u3;   // u1>u2,u3>u2,u1>u3 u1>u3>u2        else      result=u1;   // u1>u2,u3>u2,u3>u1 u3>u1>u2  else     if(u3>u2)   result=u2;     // u2>u1,u3>u2       u3>u2>u1      else        if(u1>u3) result=u3;   // u2>u1,u2>u3,u1>u3 u2>u1>u3        else      result=u1;   // u2>u1,u2>u3,u3>u1 u2>u3>u1  return(result):}unsigned char x[3],y;   // x[0] is x(n) the current sample// x[1] is x(n-1) the sample 1/fs ago// x[2] is x(n-2) the sample 2/fs agovoid sample(void){   x[2]=x[1];  // shift MACQ data   x[1]=x[0];      x[0] = A2D(0);  // new data from channel 0   y=median(x[0],x[1],x[2]); //    Program 15.7. Real time data acquisition with a 60 Hz notch digital filter, Equation 58.// MC68HC11A8#define OC5  0x08 #pragma interrupt_handler TOC5handler()void TOC5handler(void){    TFLG1=OC5;      // Ack interrupt    TOC5=TOC5+8333;  // fs=240Hz   y[2]=y[1]; y[1]=y[0];  // shift MACQ   x[2]=x[1]; x[1]=x[0];      x[0] = A2D(channel);  // new data   y[0]=(113*(x[0]+x[2])-98*y[2])>>7;}    void ritual(void) { asm(" sei");    // make atomic   TMSK1|=OC5;  // Arm output compare 5   y[0]=y[1]=y[2]=x[0]=x[1]=x[2]=0;   TFLG1=OC5;  // Initially clear OC5F   TOC5=TCNT+8333; asm(" cli"); }