DS18B20.cpp

00001 /*
00002 * DS18B20. Maxim DS18B20 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 "DS18B20.h"
00024 #include "DebugTrace.h"
00025 
00026 DebugTrace pc_ds18B20(ON, TO_SERIAL);
00027 
00028 DS18B20::DS18B20(bool crcOn, bool useAddr, bool parasitic, PinName pin) : 
00029     OneWireThermometer(crcOn, useAddr, parasitic, pin, DS18B20_ID)
00030 {
00031 }
00032 
00033 void DS18B20::setResolution(eResolution resln)
00034 {
00035     // as the write to the configuration register involves a write to the
00036     // high and low alarm bytes, need to read these registers first
00037     // and copy them back on the write
00038     
00039     BYTE read_data[THERMOM_SCRATCHPAD_SIZE];
00040     BYTE write_data[ALARM_CONFIG_SIZE];
00041     
00042     if (readAndValidateData(read_data))
00043     {
00044         // copy alarm and config data to write data
00045         for (int k = 2; k < 5; k++)
00046         {
00047             write_data[k - 2] = read_data[k];
00048         }
00049         int config = write_data[2];
00050         config &= 0x9F;
00051         config ^= (resln << 5);
00052         write_data[2] = config;
00053         
00054         resetAndAddress();
00055         oneWire.writeByte(WRITESCRATCH);
00056         for (int k = 0; k < 3; k++)
00057         {
00058             oneWire.writeByte(write_data[k]);
00059         }
00060         
00061         // remember it so we can use the correct delay in reading the temperature
00062         // for parasitic power
00063         resolution = resln; 
00064     }
00065 }
00066 
00067 float DS18B20::calculateTemperature(BYTE* data)
00068 {
00069     bool signBit = false;
00070     if (data[TEMPERATURE_MSB] & 0x80) signBit = true;
00071         
00072     int read_temp = (data[TEMPERATURE_MSB] << 8) + data[TEMPERATURE_LSB];
00073     if (signBit)
00074     {
00075         read_temp = (read_temp ^ 0xFFFF) + 1;    // two's complement
00076         read_temp *= -1;
00077     }
00078     
00079     int resolution = (data[CONFIG_REG_BYTE] & 0x60) >> 5; // mask off bits 6,5 and move to 1,0
00080     switch (resolution)
00081     {
00082         case nineBit:    // 0.5 deg C increments
00083             read_temp &= 0xFFF8;                // bits 2,1,0 are undefined
00084              pc_ds18B20.traceOut("9 bit resolution ...\r\n");
00085             break;
00086         case tenBit:     // 0.25 deg C increments
00087             read_temp &= 0xFFFC;                // bits 1,0 are undefined
00088             pc_ds18B20.traceOut("10 bit resolution ...\r\n");
00089             break;
00090         case elevenBit:  // 0.125 deg C increments
00091             read_temp &= 0xFFFE;                // bit 0 is undefined
00092             pc_ds18B20.traceOut("11 bit resolution ...\r\n");
00093             break;
00094         case twelveBit:  // 0.0625 deg C increments
00095             pc_ds18B20.traceOut("12 bit resolution ...\r\n");
00096             break;
00097     }
00098     float realTemp = (float)read_temp/16 ;
00099                  
00100     pc_ds18B20.traceOut("TEMP_READ/REAL TEMP: %f \r\n", realTemp); 
00101                
00102     return realTemp;
00103 }