DS18S20.cpp

00001 /*
00002 * DS18S20. Maxim DS18S20 One-Wire Thermometer. 
00003 * Uses the OneWireCRC library.
00004 *
00005 * Copyright (C) <2010> Petras Saduikis <petras@petras.co.uk>
00006 *
00007 * This file is part of OneWireThermometer.
00008 *
00009 * OneWireThermometer is free software: you can redistribute it and/or modify
00010 * it under the terms of the GNU General Public License as published by
00011 * the Free Software Foundation, either version 3 of the License, or
00012 * (at your option) any later version.
00013 * 
00014 * OneWireThermometer is distributed in the hope that it will be useful,
00015 * but WITHOUT ANY WARRANTY; without even the implied warranty of
00016 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00017 * GNU General Public License for more details.
00018 *
00019 * You should have received a copy of the GNU General Public License
00020 * along with OneWireThermometer.  If not, see <http://www.gnu.org/licenses/>.
00021 */
00022 
00023 #include "DS18S20.h"
00024 #include "DebugTrace.h"
00025 
00026 DebugTrace pc_ds18S20(ON, TO_SERIAL);
00027 
00028 DS18S20::DS18S20(bool crcOn, bool useAddr, bool parasitic, PinName pin) : 
00029     OneWireThermometer(crcOn, useAddr, parasitic, pin, DS18S20_ID)
00030 {
00031 }
00032 
00033 float DS18S20::calculateTemperature(BYTE* data)
00034 {    
00035     // DS18S20 basic resolution is always 9 bits, which can be enhanced as follows
00036     bool signBit = false;
00037     if (data[TEMPERATURE_MSB] & 0x80) signBit = true;
00038         
00039     int read_temp = (data[TEMPERATURE_MSB] << 8) + data[TEMPERATURE_LSB];
00040     if (signBit)
00041     {
00042         read_temp = (read_temp ^ 0xFFFF) + 1;    // two's complement
00043         read_temp *= -1;
00044     }
00045                  
00046     float readTemp = (float)read_temp/2 ;            // divide by 2
00047     pc_ds18S20.traceOut("TEMP_READ: %f \r\n", readTemp);     // 9 bit resolution value
00048                
00049     // convert to real temperature
00050     float tempCount = float(data[COUNT_PER_DEG_BYTE] - data[COUNT_REMAIN_BYTE])/(float)data[COUNT_PER_DEG_BYTE];        
00051     float realTemp = (readTemp - 0.25) + tempCount;        
00052     pc_ds18S20.traceOut("Temperature: %f \r\n", realTemp);   // enhanced resolution value
00053     
00054     return realTemp;
00055 }