chap11.c

Motorola 6808嵌入式接口设计开发原程序

// Chapter 11 6808 C programs
// Jonathan W. Valvano
// This software accompanies the book,
// Embedded Microcomputer Systems: Real Time Interfacing
// published by Brooks Cole, 1999


//  Program 11.1. Software used to test how many bits are really needed.
void DACout8(unsigned int code){ 
    DACout(code&0xFFF0);}   // ignore bottom 4 bits
void DACout10(unsigned int code){ 
    DACout(code&0xFFFC);}  // ignore bottom 2 bits

//  Program 11.2. Periodic interrupt used to create the analog output waveform.
unsigned int wave(unsigned int t){
float result,time;
time=2*pi*((float)t)/1000.0; 
// integer t in msec into floating point time in seconds
result=2048.0+1000.0*cos(31.25*time)-500.0*sin(125.0*time);
return (unsigned int) result;}


// Program 11.10. Software implementation of a ramp A/D.
unsigned int rampAD(void){ unsigned int DOUT; // guess
    DOUT = 0;             // start at minimum, V0=-5.00 (offset binary)
    do {
      DACout(DOUT);       // set D/A output, V0
      DOUT++;             // ramp
    }
    while((!Z())&&(DOUT<4096));  // stop when V0>Vin or DOUT=4096
    return(DOUT);}

// Program 11.11. Software implementation of a tracking A/D.
int DOUT; // guess
void main(void){ 
    DOUT = 2048;        // start in the middle, V0=0.00 (offset binary)
    while(1) {
      DACout(DOUT);     // set D/A output, V0
      if(Z()) {         // check input
        if(DOUT>0)      // don't go below 0
           DOUT--;      // V0>Vin so decrement
      }
      else {
        if(DOUT<4095) 
           DOUT++;      // V0<Vin so increment
      }
    }}

// Program 11.12. Interrupting software implementation of a tracking A/D.
#pragma interrupt_handler TOC5handler()
void TOC5handler(void){
   TFLG1=OC5;         // ack C5F 
   TC5=TC5+rate; 
   DACout(DOUT);      // set D/A output, V0
   if(Z()) {          // check input
      if(DOUT>0)      // don't go below 0
         DOUT--;      // V0>Vin so decrement
   }
   else {
      if(DOUT<4095) 
         DOUT++;      // V0<Vin so increment
   }
   DACout(DOUT);      // set D/A output, V0
}

// Program 11.13. Software implementation of a successive approximation A/D.
unsigned int SuccAproxAD(void){ unsigned int DOUT,bit; 
    DOUT = 0;        
    for(bit=2048;bit;bit>>1){
      DOUT |= bit;        // try to turn on this bit
      DACout(DOUT);       // set D/A output, V0
      if(Z())
        DOUT ^= bit;      // too big, so remove this bit
    }
    return(DOUT);}