TmpLM74.cpp

00001 
00002 #include "mbed.h"
00003 #include "TmpLM74.h"
00004 
00005 
00006 TmpLM74::TmpLM74(PinName mosi, PinName miso, PinName sclk, PinName csLM74):
00007         SPI(mosi, miso, sclk), _csLM74(csLM74) {
00008 
00009        _csLM74 = 1;
00010 
00011         format(8,3);            // initialize SPI peripheral
00012         frequency(1000000);     // initialize SPI peripheral
00013 
00014         startLM74();
00015     }
00016     
00017 float TmpLM74::readTemp(void){
00018 
00019     float realTemp;
00020     int16_t tempRegister;
00021     
00022     _csLM74 = 0;
00023     
00024     tempRegister = ((uint16_t) write(0xFF)) << 8;
00025     tempRegister |= write(0xFF);
00026     
00027     _csLM74 = 1;
00028     
00029 //    tempRegister = (((uint16_t) 0xE4) << 8) | 0x84; // -55.0 C
00030 //    tempRegister = (((uint16_t) 0xFB) << 8) | 0x04; // -10.0 C
00031 //    tempRegister = 0x8000;                          // power down
00032     
00033 //    pc.printf("TempRegister = 0x%x\n", tempRegister);     debugging ONLY
00034     
00035     if ((tempRegister & 0x0004) == 0) {             // temp reading NOT ready or LM74 in power down
00036         if((tempRegister & 0xFFFC) == 0x8000) {     // Manufacturer's Device ID Register (power down) ?
00037             startLM74();
00038         }
00039         tempRegister = INVALID_LM74_TEMP;
00040     } else {
00041         tempRegister >>= 3;
00042     }
00043     realTemp = ((float) tempRegister) * 0.0625;
00044     
00045     return realTemp;
00046 }
00047 //      ******************************************************************
00048 
00049 void TmpLM74::startLM74(void){
00050 
00051     _csLM74 = 0;
00052     
00053     uint8_t dummy = write(0x00);
00054     dummy = write(0x00);
00055     dummy = write(0x00);
00056     dummy = write(0x00);            // this byte sets LM74 to continuous conversion
00057     
00058     _csLM74 = 1;
00059 }
00060 //      ******************************************************************
00061 
00062 void TmpLM74::shutLM74down(void){
00063 
00064     _csLM74 = 0;
00065     
00066     uint8_t dummy = write(0xFF);
00067     dummy = write(0xFF);
00068     dummy = write(0xFF);        // these 2 bytes set LM74 to power down
00069     dummy = write(0xFF);        // these 2 bytes set LM74 to power down
00070     
00071     _csLM74 = 1;
00072 }
00073 //      ******************************************************************