DS18X20.c

00001 /**
00002 * @file DS18x20.c
00003 * @brief library of DS18X20 1-Wire digital thermometer (http://www.maxim-ic.com/datasheet/index.mvp/id/2812)
00004 * @author Maciej Rajtar (Published 10 May 2010 www.mbed.org)
00005 * @author Frederic BLANC
00006 */
00007 #include "mbed.h"
00008 #include "onewire.h"
00009 #include "DS18X20.h"
00010 #include "crc8.h"
00011 #include "utils.h"
00012 /**
00013 *     @brief get power status of DS18x20
00014 *    @param  [in] uint8_t id[] = rom_code
00015 *    @return DS18X20_POWER_EXTERN or DS18X20_POWER_PARASITE
00016 *     @date 20/06/2011
00017 */
00018 uint8_t DS18X20_get_power_status(uint8_t id[]) {
00019     uint8_t pstat;
00020     ow_reset();
00021     ow_command(DS18X20_READ_POWER_SUPPLY, id);
00022     pstat=ow_bit_io(1); // pstat 0=is parasite/ !=0 ext. powered
00023     ow_reset();
00024     return (pstat) ? DS18X20_POWER_EXTERN:DS18X20_POWER_PARASITE;
00025 }
00026 
00027 
00028 
00029 /**
00030 *   @brief start measurement (CONVERT_T) for all sensors if input id==NULL
00031    or for single sensor. then id is the rom-code
00032 *    @param  [in] uint8_t with_power_extern
00033 *    @param  [in] uint8_t id[] = rom_code
00034 *    @return DS18X20_OK or DS18X20_START_FAIL
00035 *     @date 20/06/2011
00036 */
00037 uint8_t DS18X20_start_meas( uint8_t with_power_extern, uint8_t id[]) {
00038     ow_reset(); //**
00039     if ( ow_test_pin() ) { // only send if bus is "idle" = high
00040         ow_command( DS18X20_CONVERT_T, id );
00041         if (with_power_extern != DS18X20_POWER_EXTERN)
00042             ow_parasite_enable();
00043         return DS18X20_OK;
00044     }
00045     return DS18X20_START_FAIL;
00046 
00047 }
00048 
00049 /**
00050 *   @brief reads temperature (scratchpad) of sensor with rom-code id
00051    output: subzero==1 if temp.<0, cel: full celsius, mcel: frac
00052    in millicelsius*0.1
00053    i.e.: subzero=1, cel=18, millicel=5000 = -18,5000&#65533;C
00054 *    @param  [in] id[] = rom_code
00055 *    @param  [out] subzero
00056 *    @param  [out] cel
00057 *    @param  [out] cel_frac_bits
00058 *    @return DS18X20_OK or DS18X20_ERROR_CRC
00059 *     @date 20/06/2011
00060 */
00061 uint8_t DS18X20_read_meas(uint8_t id[], uint8_t *subzero,
00062                           uint8_t *cel, uint8_t *cel_frac_bits) {
00063     uint8_t i;
00064     uint8_t sp[DS18X20_SP_SIZE];
00065 
00066     ow_reset();
00067     ow_command(DS18X20_READ, id);
00068     for ( i=0 ; i< DS18X20_SP_SIZE; i++ )
00069         sp[i]=ow_byte_rd();
00070     if ( crc8( &sp[0], DS18X20_SP_SIZE ) ){
00071           if ((sp[DS18X20_SP_SIZE-1]==0xFF) && (sp[DS18X20_SP_SIZE-2]==0xFF))
00072             return OW_ERROR;    // bus error
00073         return DS18X20_ERROR_CRC;    // data error
00074     }
00075         
00076     DS18X20_meas_to_cel(id[0], sp, subzero, cel, cel_frac_bits);
00077     return DS18X20_OK;
00078 }
00079 
00080 /**
00081 *   @brief convert raw value from DS18x20 to Celsius
00082    input is:
00083    - familycode fc (0x10/0x28 see header)
00084    - scratchpad-buffer
00085    output is:
00086    - cel full celsius
00087    - fractions of celsius in millicelsius*(10^-1)/625 (the 4 LS-Bits)
00088    - subzero =0 positiv / 1 negativ
00089    always returns  DS18X20_OK
00090    TODO invalid-values detection (but should be covered by CRC)
00091 *    @param  [in] fc
00092 *    @param  [in] sp
00093 *    @param  [out] subzero
00094 *    @param  [out] cel
00095 *    @param  [out] cel_frac_bits
00096 *    @return DS18X20_OK
00097 *     @date 20/06/2011
00098 */
00099 uint8_t DS18X20_meas_to_cel( uint8_t fc, uint8_t *sp,
00100                              uint8_t* subzero, uint8_t* cel, uint8_t* cel_frac_bits) {
00101     uint16_t meas;
00102     uint8_t  i;
00103 
00104     meas = sp[0];  // LSB
00105     meas |= ((uint16_t)sp[1])<<8; // MSB
00106     //meas = 0xff5e; meas = 0xfe6f;
00107 
00108     //  only work on 12bit-base
00109     if ( fc == DS18S20_ID ) { // 9 -> 12 bit if 18S20
00110         /* Extended measurements for DS18S20 contributed by Carsten Foss */
00111         meas &= (uint16_t) 0xfffe;    // Discard LSB , needed for later extended precicion calc
00112         meas <<= 3;                    // Convert to 12-bit , now degrees are in 1/16 degrees units
00113         meas += (16 - sp[6]) - 4;    // Add the compensation , and remember to subtract 0.25 degree (4/16)
00114     }
00115 
00116     // check for negative
00117     if ( meas & 0x8000 )  {
00118         *subzero=1;      // mark negative
00119         meas ^= 0xffff;  // convert to positive => (twos complement)++
00120         meas++;
00121     } else *subzero=0;
00122 
00123     // clear undefined bits for B != 12bit
00124     if ( fc == DS18B20_ID ) { // check resolution 18B20
00125         i = sp[DS18B20_CONF_REG];
00126         if ( (i & DS18B20_12_BIT) == DS18B20_12_BIT ) ;
00127         else if ( (i & DS18B20_11_BIT) == DS18B20_11_BIT )
00128             meas &= ~(DS18B20_11_BIT_UNDF);
00129         else if ( (i & DS18B20_10_BIT) == DS18B20_10_BIT )
00130             meas &= ~(DS18B20_10_BIT_UNDF);
00131         else { // if ( (i & DS18B20_9_BIT) == DS18B20_9_BIT ) {
00132             meas &= ~(DS18B20_9_BIT_UNDF);
00133         }
00134     }
00135 
00136     *cel  = (uint8_t)(meas >> 4);
00137     *cel_frac_bits = (uint8_t)(meas & 0x000F);
00138 
00139     return DS18X20_OK;
00140 }
00141 
00142 /**
00143 *   @brief converts to decicelsius
00144    input is ouput from meas_to_cel
00145     i.e.: sz=0, c=28, frac=15 returns 289 (=28.9&#65533;C)
00146 0    0    0
00147 1    625    625    1
00148 2    1250    250
00149 3    1875    875    3
00150 4    2500    500    4
00151 5    3125    125
00152 6    3750    750    6
00153 7    4375    375
00154 8    5000    0
00155 9    5625    625    9
00156 10    6250    250
00157 11    6875    875    11
00158 12    7500    500    12
00159 13    8125    125
00160 14    8750    750    14
00161 15    9375    375
00162 *    @param  [in]  subzero
00163 *    @param  [in]  cel
00164 *    @param  [in]  cel_frac_bits
00165 *    @return absolute value of temperatur in decicelsius
00166 *     @date 20/06/2011
00167 */
00168 uint16_t DS18X20_temp_to_decicel(uint8_t subzero, uint8_t cel,
00169                                  uint8_t cel_frac_bits) {
00170     uint16_t h;
00171     uint8_t  i;
00172     uint8_t need_rounding[] = { 1, 3, 4, 6, 9, 11, 12, 14 };
00173 
00174     h = cel_frac_bits*DS18X20_FRACCONV/1000;
00175     h += cel*10;
00176     if (!subzero) {
00177         for (i=0; i<sizeof(need_rounding); i++) {
00178             if ( cel_frac_bits == need_rounding[i] ) {
00179                 h++;
00180                 break;
00181             }
00182         }
00183     }
00184     return h;
00185 }
00186 /**
00187 *   @brief  compare temperature values (full celsius only)
00188 *    @param  [in] subzero1
00189 *    @param  [in] cel1
00190 *    @param  [in] subzero2
00191 *    @param  [in] cel2
00192 *    @return -1 if param-pair1 < param-pair2
00193             0 if ==
00194             1 if >
00195 *     @date 20/06/2011
00196 */
00197 int8_t DS18X20_temp_cmp(uint8_t subzero1, uint16_t cel1,
00198                         uint8_t subzero2, uint16_t cel2) {
00199     int16_t t1 = (subzero1) ? (cel1*(-1)) : (cel1);
00200     int16_t t2 = (subzero2) ? (cel2*(-1)) : (cel2);
00201 
00202     if (t1<t2) return -1;
00203     if (t1>t2) return 1;
00204     return 0;
00205 }