chap7.c

Motorola 6808嵌入式接口设计开发原程序

// Chapter 7 6808 C programs
// Jonathan W. Valvano
// This software accompanies the book,
// Embedded Microcomputer Systems: Real Time Interfacing
// published by Brooks Cole, 1999



// Program 7.19. C language initialization for a D/A interface using the SPI.
// MC68HC708XL36
void DACInit(void){ // PTF0=LD=1
  DDRF|=0x07;  // PTF1=CLK=SPI clock out
  PORTF|=0x01; // PTF2=SRI=SPI master out
/* bit SPCR
 7 SPRIE  = 0   no receive interrupts
 6 DMAS   = 0   no DMA
 5 SPMSTR = 1   master
 4 CPOL   = 0   output changes on fall, 
 3 CPHA   = 0   clock normally low
 2 SPWOM  = 0   regular outputs
 1 SPE    = 1   enable SPI
 0 SPTIE  = 0   no transmit interrupts */
    SPCR=0x42;
    SPSCR=0x00;} // 2 MHz clock

// Program 7.20. C language function for a D/A interface using the SPI.
// MC68HC708XL36
#define SPRF 0x80
void DACout(unsigned int code){ 
unsigned char dummy;
   SPDR=0x00FF &(code>>8); // msbyte
   while((SPSCR&SPRF)==0); // gadfly wait 
   dummy=SPDR;            // clear SPIF
   SPDR=0x00FF& code;     // lsbyte
   while((SPSCR&SPRF)==0); // gadfly wait 
   dummy=SPDR;            // clear SPIF
   PORTF &= ~0x01;        // PTF0=LD=0
   PORTF |= 0x01; }       // PTF0=LD=1

// Program 7.21. C language initialization for an A/D interface using the SPI.
// MC68HC708XL36
void ADCInit(void){ // PTF0=CS=1
  DDRF|=0x07;  // PTF1=SCLK=SPI clock out
  PORTF|=0x01; // PTF2=DIN=SPI master out
/* bit SPCR       PTF3=DOUT=SPI master in
 7 SPRIE  = 0   no receive interrupts
 6 DMAS   = 0   no DMA
 5 SPMSTR = 1   master
 4 CPOL   = 0   output changes on fall, 
 3 CPHA   = 0   clock normally low
 2 SPWOM  = 0   regular outputs
 1 SPE    = 1   enable SPI
 0 SPTIE  = 0   no transmit interrupts */
    SPCR=0x42;
    SPSCR=0x00;} // 2 MHz clock 
#define CH0 0x9F
#define CH1 0xDF
#define CH2 0xAF
#define CH3 0xEF

// Program 7.22. C language function for an A/D interface using the SPI.
// MC68HC708XL36
unsigned int ADCin(unsigned char code){ 
unsigned int data;
   PORTF &= ~0x01; // PTF0=CS=0
   SPDR=code;    // set channel,mode
   while((SPSCR&0x80)==0); // gadfly wait 
   data=SPDR;    // clear SPIF
   SPDR=0;       // start SPI
   while((SPSCR&0x80)==0); // gadfly wait 
   data=SPDR<<8; // msbyte of A/D
   SPDR=0;       // start SPI
   while((SP0SR&0x80)==0); // gadfly wait 
   data+=SPDR;    // lsbyte of A/D
   PORTF |= 0x01; // PTF0=CS=1
   return data>>3;} // right justify

// Program 7.23. C language initialization of a temperature sensor interface using the SPI.
// MC68HC812A4/MC68HC912B32 only

// Program 7.24. C language helper functions for a temperature sensor interface using the SPI.
// MC68HC812A4/MC68HC912B32 only

// Program 7.25. C language functions for a temperature sensor interface using the SPI.
// MC68HC812A4/MC68HC912B32 only