DS1820.cpp

00001 #include "DS1820.h"
00002 #include "mbed.h"
00003 
00004 // Global variables shared between all DS1820 objects
00005 bool DS1820_done_flag;
00006 int  DS1820_last_descrepancy;
00007 char DS1820_search_ROM[8];
00008 
00009 
00010 DS1820::DS1820 (PinName data_pin, PinName power_pin) : _datapin(data_pin), _parasitepin(power_pin) {
00011     int byte_counter;
00012 
00013     _parasite_power = true;
00014     for(byte_counter=0;byte_counter<8;byte_counter++)
00015         ROM[byte_counter] = 0xFF;
00016     for(byte_counter=0;byte_counter<9;byte_counter++)
00017         RAM[byte_counter] = 0x00;
00018 }
00019 DS1820::DS1820 (PinName data_pin) : _datapin(data_pin), _parasitepin(NC) {
00020     int byte_counter;
00021     _parasite_power = false;
00022     for(byte_counter=0;byte_counter<8;byte_counter++)
00023         ROM[byte_counter] = 0xFF;
00024     for(byte_counter=0;byte_counter<9;byte_counter++)
00025         RAM[byte_counter] = 0x00; 
00026 }
00027 
00028 bool DS1820::onewire_reset() {
00029 // This will return false if no devices are present on the data bus
00030     bool presence=false;
00031     _datapin.output();
00032     _datapin.mode(PullUp);
00033     _datapin = 0;           // bring low for 500 us
00034     wait_us(500);
00035     _datapin.input();       // let the data line float high
00036     _datapin.mode(PullUp);
00037     wait_us(90);            // wait 90us
00038     if (_datapin.read()==0) // see if any devices are pulling the data line low
00039         presence=true;
00040     wait_us(410);
00041     return presence;
00042 }
00043 
00044 void DS1820::onewire_bit_out (bool bit_data) {
00045     _datapin.output();
00046     _datapin = 0;
00047     wait_us(5);
00048     if (bit_data) {
00049         _datapin.input(); // bring data line high
00050         _datapin.mode(PullUp);
00051         wait_us(55);
00052     } else {
00053         wait_us(55);            // keep data line low
00054         _datapin.input();
00055         _datapin.mode(PullUp);
00056     }
00057 }
00058 
00059 void DS1820::onewire_byte_out(char data) { // output data character (least sig bit first).
00060     int n;
00061     for (n=0; n<8; n++) {
00062         onewire_bit_out(data & 0x01);
00063         data = data >> 1; // now the next bit is in the least sig bit position.
00064     }
00065 }
00066 
00067 bool DS1820::onewire_bit_in() {
00068     bool answer;
00069     _datapin.output();
00070     _datapin = 0;
00071     wait_us(5);
00072     _datapin.input();
00073     _datapin.mode(PullUp);
00074     wait_us(5);
00075     answer = _datapin.read();
00076     wait_us(50);
00077     return answer;
00078 }
00079 
00080 char DS1820::onewire_byte_in() { // read byte, least sig byte first
00081     char answer = 0x00;
00082     int i;
00083     for (i=0; i<8; i++) {
00084         answer = answer >> 1; // shift over to make room for the next bit
00085         if (onewire_bit_in())
00086             answer = answer | 0x80; // if the data port is high, make this bit a 1
00087     }
00088     return answer;
00089 }
00090 
00091 bool DS1820::search_ROM() {
00092     return search_ROM_routine(0xF0);    // Search ROM command
00093 }
00094 
00095 bool DS1820::search_alarm() {
00096     return search_ROM_routine(0xEC);    // Search Alarm command
00097 }
00098 
00099 bool DS1820::search_ROM_routine(char command) {
00100     extern bool DS1820_done_flag;
00101     extern int DS1820_last_descrepancy;
00102     extern char DS1820_search_ROM[8];
00103     int descrepancy_marker, ROM_bit_index;
00104     bool return_value, Bit_A, Bit_B;
00105     char byte_counter, bit_mask;
00106 
00107     return_value=false;
00108     if (!DS1820_done_flag) {
00109         if (!onewire_reset()) {
00110             DS1820_last_descrepancy = 0; // no devices present
00111         } else {
00112             ROM_bit_index=1;
00113             descrepancy_marker=0;
00114             onewire_byte_out(command); // Search ROM command or Search Alarm command
00115             byte_counter = 0;
00116             bit_mask = 0x01;
00117             while (ROM_bit_index<=64) {
00118                 Bit_A = onewire_bit_in();
00119                 Bit_B = onewire_bit_in();
00120                 if (Bit_A & Bit_B) {
00121                     descrepancy_marker = 0; // data read error, this should never happen
00122                     ROM_bit_index = 0xFF;
00123                 } else {
00124                     if (Bit_A | Bit_B) {
00125                         // Set ROM bit to Bit_A
00126                         if (Bit_A) {
00127                             DS1820_search_ROM[byte_counter] = DS1820_search_ROM[byte_counter] | bit_mask; // Set ROM bit to one
00128                         } else {
00129                             DS1820_search_ROM[byte_counter] = DS1820_search_ROM[byte_counter] & ~bit_mask; // Set ROM bit to zero
00130                         }
00131                     } else {
00132                         // both bits A and B are low, so there are two or more devices present
00133                         if ( ROM_bit_index == DS1820_last_descrepancy ) {
00134                             DS1820_search_ROM[byte_counter] = DS1820_search_ROM[byte_counter] | bit_mask; // Set ROM bit to one
00135                         } else {
00136                             if ( ROM_bit_index > DS1820_last_descrepancy ) {
00137                                 DS1820_search_ROM[byte_counter] = DS1820_search_ROM[byte_counter] & ~bit_mask; // Set ROM bit to zero
00138                                 descrepancy_marker = ROM_bit_index;
00139                             } else {
00140                                 if (( DS1820_search_ROM[byte_counter] & bit_mask) == 0x00 )
00141                                     descrepancy_marker = ROM_bit_index;
00142                             }
00143                         }
00144                     }
00145                     onewire_bit_out (DS1820_search_ROM[byte_counter] & bit_mask);
00146                     ROM_bit_index++;
00147                     if (bit_mask & 0x80) {
00148                         byte_counter++;
00149                         bit_mask = 0x01;
00150                     } else {
00151                         bit_mask = bit_mask << 1;
00152                     }
00153                 }
00154             }
00155             DS1820_last_descrepancy = descrepancy_marker;
00156             if (ROM_bit_index != 0xFF) {
00157                 for(byte_counter=0;byte_counter<8;byte_counter++)
00158                     ROM[byte_counter] = DS1820_search_ROM[byte_counter];
00159                 return_value = true;
00160             }
00161         }
00162         if (DS1820_last_descrepancy == 0)
00163             DS1820_done_flag = true;
00164     }
00165     return return_value;
00166 }
00167 
00168 void DS1820::search_ROM_setup() {
00169     extern bool DS1820_done_flag;
00170     extern int DS1820_last_descrepancy;
00171     extern char DS1820_search_ROM[8];
00172     DS1820_done_flag = false;
00173     DS1820_last_descrepancy = 0;
00174     int i;
00175     for (i=0; i<8; i++)
00176         DS1820_search_ROM[i]=0x00;
00177 }
00178 
00179 void DS1820::read_ROM() {
00180     // NOTE: This command can only be used when there is one DS1820 on the bus. If this command
00181     // is used when there is more than one slave present on the bus, a data collision will occur
00182     // when all the DS1820s attempt to respond at the same time.
00183     int i;
00184     onewire_reset();
00185     onewire_byte_out(0x33);   // Read ROM id
00186     for (i=0; i<8; i++)
00187         ROM[i]=onewire_byte_in();
00188 }
00189 
00190 void DS1820::match_ROM() {
00191 // Used to select a specific device
00192     int i;
00193     onewire_reset();
00194     onewire_byte_out( 0x55);  //Match ROM command
00195     for (i=0;i<8;i++)
00196         onewire_byte_out(ROM[i]);
00197 }
00198 
00199 void DS1820::skip_ROM() {
00200     onewire_reset();
00201     onewire_byte_out(0xCC);   // Skip ROM command
00202 }
00203 
00204 bool DS1820::ROM_checksum_error() {
00205     char xCRC=0x00;
00206     int i;
00207     for(i=0;i<7;i++) // Only going to shift the lower 7 bytes
00208         xCRC = CRC_byte(xCRC, ROM[i]);
00209     // After 7 bytes CRC should equal the 8th byte (ROM CRC)
00210     return (xCRC!=ROM[7]); // will return true if there is a CRC checksum error         
00211 }
00212 
00213 bool DS1820::RAM_checksum_error() {
00214     char xCRC=0x00;
00215     int i;
00216     read_RAM();
00217     for(i=0;i<8;i++) // Only going to shift the lower 8 bytes
00218         xCRC = CRC_byte(xCRC, RAM[i]);
00219     // After 8 bytes CRC should equal the 9th byte (RAM CRC)
00220     return (xCRC!=RAM[8]); // will return true if there is a CRC checksum error         
00221 }
00222 
00223 char DS1820::CRC_byte (char xCRC, char byte ) {
00224     int j;
00225     for(j=0;j<8;j++) {
00226         if ((byte & 0x01 ) ^ (xCRC & 0x01)) {
00227             // DATA ^ LSB CRC = 1
00228             xCRC = xCRC>>1;
00229             // Set the MSB to 1
00230             xCRC = xCRC | 0x80;
00231             // Check bit 3
00232             if (xCRC & 0x04) {
00233                 xCRC = xCRC & 0xFB; // Bit 3 is set, so clear it
00234             } else {
00235                 xCRC = xCRC | 0x04; // Bit 3 is clear, so set it
00236             }
00237             // Check bit 4
00238             if (xCRC & 0x08) {
00239                 xCRC = xCRC & 0xF7; // Bit 4 is set, so clear it
00240             } else {
00241                 xCRC = xCRC | 0x08; // Bit 4 is clear, so set it
00242             }
00243         } else {
00244             // DATA ^ LSB xCRC = 0
00245             xCRC = xCRC>>1;
00246             // clear MSB
00247             xCRC = xCRC & 0x7F;
00248             // No need to check bits, with DATA ^ LSB xCRC = 0, they will remain unchanged
00249         }
00250         byte = byte>>1;
00251     }
00252 return xCRC;
00253 }
00254 
00255 void DS1820::convert_temperature(devices device) {
00256     // Convert temperature into scratchpad RAM for all devices at once
00257     int delay_time = 750; // Default delay time
00258     char resolution;
00259     if (device==all_devices)
00260         skip_ROM();          // Skip ROM command, will convert for ALL devices
00261     else {
00262         match_ROM();
00263         if (FAMILY_CODE == FAMILY_CODE_DS18B20 ) {
00264             resolution = RAM[4] & 0x60;
00265             if (resolution == 0x00) // 9 bits
00266                 delay_time = 94;
00267             if (resolution == 0x20) // 10 bits
00268                 delay_time = 188;
00269             if (resolution == 0x40) // 11 bits. Note 12bits uses the 750ms default
00270                 delay_time = 375;
00271         }
00272     }
00273     onewire_byte_out( 0x44);  // perform temperature conversion
00274     if (_parasite_power)
00275         _parasitepin = 1;       // Parasite power strong pullup
00276     wait_ms(delay_time);
00277     if (_parasite_power)
00278         _parasitepin = 0;
00279 }
00280 
00281 void DS1820::read_RAM() {
00282     // This will copy the DS1820's 9 bytes of RAM data
00283     // into the objects RAM array. Functions that use
00284     // RAM values will automaticly call this procedure.
00285     int i;
00286     match_ROM();             // Select this device
00287     onewire_byte_out( 0xBE);   //Read Scratchpad command
00288     for(i=0;i<9;i++) {
00289         RAM[i] = onewire_byte_in();
00290     }
00291 }
00292 
00293 bool DS1820::set_configuration_bits(unsigned int resolution) {
00294     bool answer = false;
00295     resolution = resolution - 9;
00296     if (resolution < 4) {
00297         resolution = resolution<<5; // align the bits
00298         RAM[4] = (RAM[4] & 0x60) | resolution; // mask out old data, insert new
00299         write_scratchpad ((RAM[2]<<8) + RAM[3]);
00300 //        store_scratchpad (DS1820::this_device); // Need to test if this is required
00301         answer = true;
00302     }
00303     return answer;
00304 }
00305 
00306 int DS1820::read_scratchpad() {
00307     int answer;
00308     read_RAM();
00309     answer = (RAM[2]<<8) + RAM[3];
00310     return answer;
00311 }
00312 
00313 void DS1820::write_scratchpad(int data) {
00314     RAM[3] = data;
00315     RAM[2] = data>>8;
00316     match_ROM();
00317     onewire_byte_out(0x4E);   // Copy scratchpad into DS1820 ram memory
00318     onewire_byte_out(RAM[2]); // T(H)
00319     onewire_byte_out(RAM[3]); // T(L)
00320     if ( FAMILY_CODE == FAMILY_CODE_DS18B20 ) {
00321         onewire_byte_out(RAM[4]); // Configuration register
00322     }
00323 }
00324 
00325 void DS1820::store_scratchpad(devices device) {
00326     if (device==all_devices)
00327         skip_ROM();          // Skip ROM command, will store for ALL devices
00328     else
00329         match_ROM();
00330     onewire_byte_out(0x48);   // Write scratchpad into E2 command
00331     if (_parasite_power)
00332         _parasitepin=1;
00333     wait_ms(10);            // Parasite power strong pullup for 10ms
00334     if (_parasite_power)
00335         _parasitepin=0;
00336 }
00337 
00338 int DS1820::recall_scratchpad(devices device) {
00339 // This copies the E2 values into the DS1820's memory.
00340 // If you specify all_devices this will return zero, otherwise
00341 // it will return the value of the scratchpad memory.
00342     int answer=0;
00343     if (device==all_devices)
00344         skip_ROM();          // Skip ROM command, will recall for ALL devices
00345     else
00346         match_ROM();
00347     onewire_byte_out(0xB8);   // Recall E2 data to scratchpad command
00348     wait_ms(10); // not sure I like polling for completion
00349                  // it could cause an infinite loop
00350     if (device==DS1820::this_device) {
00351         read_RAM();
00352         answer = read_scratchpad();
00353     }
00354     return answer;
00355 }    
00356 
00357 float DS1820::temperature(char scale) {
00358 // The data specs state that count_per_degree should be 0x10 (16), I found my devices
00359 // to have a count_per_degree of 0x4B (75). With the standard resolution of 1/2 deg C
00360 // this allowed an expanded resolution of 1/150th of a deg C. I wouldn't rely on this
00361 // being super acurate, but it does allow for a smooth display in the 1/10ths of a
00362 // deg C or F scales.
00363     float answer, remaining_count, count_per_degree;
00364     int reading;
00365     read_RAM();
00366     reading = (RAM[1] << 8) + RAM[0];
00367     if (reading & 0x8000) { // negative degrees C
00368         reading = 0-((reading ^ 0xffff) + 1); // 2's comp then convert to signed int
00369     }
00370     answer = reading +0.0; // convert to floating point
00371     if ( FAMILY_CODE == FAMILY_CODE_DS18B20 ) {
00372         answer = answer / 8.0;
00373     }
00374     else {
00375         remaining_count = RAM[6];
00376         count_per_degree = RAM[7];
00377         answer = answer - 0.25 + (count_per_degree - remaining_count) / count_per_degree;
00378     }
00379     if (scale=='C' or scale=='c')
00380         answer = answer / 2.0;
00381     else
00382         // Convert to deg F
00383         answer = answer * 9.0 / 10.0 + 32.0;
00384     return answer;
00385 }
00386 
00387 bool DS1820::read_power_supply(devices device) {
00388 // This will return true if the device (or all devices) are Vcc powered
00389 // This will return false if the device (or ANY device) is parasite powered
00390     if (device==all_devices)
00391         skip_ROM();          // Skip ROM command, will poll for any device using parasite power
00392     else
00393         match_ROM();
00394     onewire_byte_out(0xB4);   // Read power supply command
00395     return onewire_bit_in();
00396 }