ds1722_spi_tempsense.c - SPI example: PIC24 uC in Master mode to Maxim DS1722 Digital Thermometer

 
#include "pic24_all.h"
#include <stdio.h>

#define CONFIG_SLAVE_ENABLE() CONFIG_RB3_AS_DIG_OUTPUT()
#define SLAVE_ENABLE()        _LATB3 = 1  //high true assertion
#define SLAVE_DISABLE()       _LATB3 = 0

void configSPI1(void) {
  SPI1CON1 =
#if (defined(__dsPIC33E__) || defined(__PIC24E__))
    //spi clock = 60MHz/1*6 = 60MHz/4 = 10MHz
    PRI_PRESCAL_1_1 |     //1:1 primary prescale
    SEC_PRESCAL_6_1 |     //6:1 secondary prescale
#else
    //spi clock = 40MHz/4*1 = 40MHz/4 = 10MHz
    PRI_PRESCAL_4_1 |     //4:1 primary prescale
    SEC_PRESCAL_1_1 |     //1:1 secondary prescale
#endif
    CLK_POL_ACTIVE_HIGH   | //clock active high (CKP = 0)
    SPI_CKE_OFF          | //out changes inactive to active (CKE=0)
    SPI_MODE8_ON        | //8-bit mode
    MASTER_ENABLE_ON;     //master mode
#if (defined(__dsPIC33E__) || defined(__PIC24E__))
  //nothing to do here. On this family, the SPI1 port uses dedicated
  //pins for higher speed. The SPI2 port can be used with remappable pins.
#else
//all other families (PIC24H/PIC24F/dsPIC33F)
  CONFIG_SDO1_TO_RP(RB6_RP);      //use RB6 for SDO
  CONFIG_RB6_AS_DIG_OUTPUT();   //Ensure that this is a digital output
  CONFIG_SCK1OUT_TO_RP(RB7_RP);   //use RB7 for SCLK
  CONFIG_RB7_AS_DIG_INPUT();   //Ensure that this is a digital input
  CONFIG_SDI1_TO_RP(RB5_RP);      //use RP5 for SDI
  CONFIG_RB5_AS_DIG_INPUT();   //Ensure that this is a digital input
#endif
  CONFIG_SLAVE_ENABLE();       //chip select for MCP41xxx
  SLAVE_DISABLE();             //disable the chip select
  SPI1STATbits.SPIEN = 1;  //enable SPI mode
}

void writeConfigDS1722(uint8_t u8_i) {
  SLAVE_ENABLE();       //assert chipselect
  ioMasterSPI1(0x80);   //config address
  ioMasterSPI1(u8_i);   //config value
  SLAVE_DISABLE();
}

int16_t readTempDS1722() {
  uint16_t u16_lo, u16_hi;
  SLAVE_ENABLE();       //assert chipselect
  ioMasterSPI1(0x01);   //LSB address
  u16_lo = ioMasterSPI1(0x00); //read LSByte
  u16_hi = ioMasterSPI1(0x00); //read MSByte
  SLAVE_DISABLE();
  return((u16_hi<<8) | u16_lo);
}

int main (void) {
  int16_t i16_temp;
  float  f_tempC,f_tempF;
  configBasic(HELLO_MSG);
  configSPI1();
  writeConfigDS1722(0xE8); //10-bit mode
  while (1) {
    DELAY_MS(1500);
    i16_temp = readTempDS1722();
    f_tempC = i16_temp;  //convert to floating point
    f_tempC = f_tempC/256;  //divide by precision
    f_tempF = f_tempC*9/5 + 32;
    printf("Temp is: 0x%0X, %4.4f (C), %4.4f (F)\n", i16_temp, (double) f_tempC, (double) f_tempF);
  }
}