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     _parasite_power = true;
00013     for(byte_counter=0;byte_counter<8;byte_counter++)
00014         ROM[byte_counter] = 0xFF;
00015     for(byte_counter=0;byte_counter<9;byte_counter++)
00016         RAM[byte_counter] = 0x00;
00017 }
00018 DS1820::DS1820 (PinName data_pin) : _datapin(data_pin), _parasitepin(NC) {
00019     int byte_counter;
00020     _parasite_power = false;
00021     for(byte_counter=0;byte_counter<8;byte_counter++)
00022         ROM[byte_counter] = 0xFF;
00023     for(byte_counter=0;byte_counter<9;byte_counter++)
00024         RAM[byte_counter] = 0x00;
00025 }
00026  
00027 bool DS1820::onewire_reset() {
00028 // This will return false if no devices are present on the data bus
00029     bool presence=false;
00030     _datapin.output();
00031     _datapin = 0;           // bring low for 500 us
00032     wait_us(500);
00033     _datapin.input();       // let the data line float high
00034     wait_us(90);            // wait 90us
00035     if (_datapin.read()==0) // see if any devices are pulling the data line low
00036         presence=true;
00037     wait_us(410);
00038     return presence;
00039 }
00040  
00041 void DS1820::onewire_bit_out (bool bit_data) {
00042     _datapin.output();
00043     _datapin = 0;
00044     wait_us(3);                 // DXP modified from 5
00045     if (bit_data) {
00046         _datapin.input(); // bring data line high
00047         wait_us(55);
00048     } else {
00049         wait_us(55);            // keep data line low
00050         _datapin.input();
00051         wait_us(10);            // DXP added to allow bus to float high before next bit_out
00052     }
00053 }
00054  
00055 void DS1820::onewire_byte_out(char data) { // output data character (least sig bit first).
00056     int n;
00057     for (n=0; n<8; n++) {
00058         onewire_bit_out(data & 0x01);
00059         data = data >> 1; // now the next bit is in the least sig bit position.
00060     }
00061 }
00062  
00063 bool DS1820::onewire_bit_in() {
00064     bool answer;
00065     _datapin.output();
00066     _datapin = 0;
00067     wait_us(3);                 // DXP modofied from 5
00068     _datapin.input();
00069     wait_us(10);                // DXP modified from 5
00070     answer = _datapin.read();
00071     wait_us(45);                // DXP modified from 50
00072     return answer;
00073 }
00074  
00075 char DS1820::onewire_byte_in() { // read byte, least sig byte first
00076     char answer = 0x00;
00077     int i;
00078     for (i=0; i<8; i++) {
00079         answer = answer >> 1; // shift over to make room for the next bit
00080         if (onewire_bit_in())
00081             answer = answer | 0x80; // if the data port is high, make this bit a 1
00082     }
00083     return answer;
00084 }
00085  
00086 bool DS1820::search_ROM() {
00087     return search_ROM_routine(0xF0);    // Search ROM command
00088 }
00089  
00090 bool DS1820::search_alarm() {
00091     return search_ROM_routine(0xEC);    // Search Alarm command
00092 }
00093  
00094 bool DS1820::search_ROM_routine(char command) {
00095     extern bool DS1820_done_flag;
00096     extern int DS1820_last_descrepancy;
00097     extern char DS1820_search_ROM[8];
00098     int descrepancy_marker, ROM_bit_index;
00099     bool return_value, Bit_A, Bit_B;
00100     char byte_counter, bit_mask;
00101  
00102     return_value=false;
00103     if (!DS1820_done_flag) {
00104         if (!onewire_reset()) {
00105             DS1820_last_descrepancy = 0; // no devices present
00106         } else {
00107             ROM_bit_index=1;
00108             descrepancy_marker=0;
00109             onewire_byte_out(command); // Search ROM command or Search Alarm command
00110             byte_counter = 0;
00111             bit_mask = 0x01;
00112             while (ROM_bit_index<=64) {
00113                 Bit_A = onewire_bit_in();
00114                 Bit_B = onewire_bit_in();
00115                 if (Bit_A & Bit_B) {
00116                     descrepancy_marker = 0; // data read error, this should never happen
00117                     ROM_bit_index = 0xFF;
00118                 } else {
00119                     if (Bit_A | Bit_B) {
00120                         // Set ROM bit to Bit_A
00121                         if (Bit_A) {
00122                             DS1820_search_ROM[byte_counter] = DS1820_search_ROM[byte_counter] | bit_mask; // Set ROM bit to one
00123                         } else {
00124                             DS1820_search_ROM[byte_counter] = DS1820_search_ROM[byte_counter] & ~bit_mask; // Set ROM bit to zero
00125                         }
00126                     } else {
00127                         // both bits A and B are low, so there are two or more devices present
00128                         if ( ROM_bit_index == DS1820_last_descrepancy ) {
00129                             DS1820_search_ROM[byte_counter] = DS1820_search_ROM[byte_counter] | bit_mask; // Set ROM bit to one
00130                         } else {
00131                             if ( ROM_bit_index > DS1820_last_descrepancy ) {
00132                                 DS1820_search_ROM[byte_counter] = DS1820_search_ROM[byte_counter] & ~bit_mask; // Set ROM bit to zero
00133                                 descrepancy_marker = ROM_bit_index;
00134                             } else {
00135                                 if (( DS1820_search_ROM[byte_counter] & bit_mask) == 0x00 )
00136                                     descrepancy_marker = ROM_bit_index;
00137                             }
00138                         }
00139                     }
00140                     onewire_bit_out (DS1820_search_ROM[byte_counter] & bit_mask);
00141                     ROM_bit_index++;
00142                     if (bit_mask & 0x80) {
00143                         byte_counter++;
00144                         bit_mask = 0x01;
00145                     } else {
00146                         bit_mask = bit_mask << 1;
00147                     }
00148                 }
00149             }
00150             DS1820_last_descrepancy = descrepancy_marker;
00151             if (ROM_bit_index != 0xFF) {
00152                 for(byte_counter=0;byte_counter<8;byte_counter++)
00153                     ROM[byte_counter] = DS1820_search_ROM[byte_counter];
00154                 if (ROM_checksum_error())           // Check the CRC
00155                     DS1820_last_descrepancy = 0;    // Abort any more search
00156                 else
00157                     return_value = true;
00158             }
00159         }
00160         if (DS1820_last_descrepancy == 0)
00161             DS1820_done_flag = true;
00162     }
00163     return return_value;
00164 }
00165  
00166 void DS1820::search_ROM_setup() {
00167     extern bool DS1820_done_flag;
00168     extern int DS1820_last_descrepancy;
00169     extern char DS1820_search_ROM[8];
00170     DS1820_done_flag = false;
00171     DS1820_last_descrepancy = 0;
00172     int i;
00173     for (i=0; i<8; i++)
00174         DS1820_search_ROM[i]=0x00;
00175 }
00176  
00177 void DS1820::read_ROM() {
00178     // NOTE: This command can only be used when there is one DS1820 on the bus. If this command
00179     // is used when there is more than one slave present on the bus, a data collision will occur
00180     // when all the DS1820s attempt to respond at the same time.
00181     int i;
00182     onewire_reset();
00183     onewire_byte_out(0x33);   // Read ROM id
00184     for (i=0; i<8; i++)
00185         ROM[i]=onewire_byte_in();
00186 }
00187  
00188 void DS1820::match_ROM() {
00189 // Used to select a specific device
00190     int i;
00191     onewire_reset();
00192     onewire_byte_out( 0x55);  //Match ROM command
00193     for (i=0;i<8;i++)
00194         onewire_byte_out(ROM[i]);
00195 }
00196  
00197 void DS1820::skip_ROM() {
00198     onewire_reset();
00199     onewire_byte_out(0xCC);   // Skip ROM command
00200 }
00201  
00202 bool DS1820::ROM_checksum_error() {
00203     char CRC=0x00;
00204     int i;
00205     for(i=0;i<7;i++) // Only going to shift the lower 7 bytes
00206         CRC = CRC_byte(CRC, ROM[i]);
00207     // After 7 bytes CRC should equal the 8th byte (ROM CRC)
00208     return (CRC!=ROM[7]); // will return true if there is a CRC checksum mis-match         
00209 }
00210  
00211 bool DS1820::RAM_checksum_error() {
00212     char CRC=0x00;
00213     int i;
00214     for(i=0;i<8;i++) // Only going to shift the lower 8 bytes
00215         CRC = CRC_byte(CRC, RAM[i]);
00216     // After 8 bytes CRC should equal the 9th byte (RAM CRC)
00217     return (CRC!=RAM[8]); // will return true if there is a CRC checksum mis-match        
00218 }
00219  
00220 char DS1820::CRC_byte (char CRC, char byte ) {
00221     int j;
00222     for(j=0;j<8;j++) {
00223         if ((byte & 0x01 ) ^ (CRC & 0x01)) {
00224             // DATA ^ LSB CRC = 1
00225             CRC = CRC>>1;
00226             // Set the MSB to 1
00227             CRC = CRC | 0x80;
00228             // Check bit 3
00229             if (CRC & 0x04) {
00230                 CRC = CRC & 0xFB; // Bit 3 is set, so clear it
00231             } else {
00232                 CRC = CRC | 0x04; // Bit 3 is clear, so set it
00233             }
00234             // Check bit 4
00235             if (CRC & 0x08) {
00236                 CRC = CRC & 0xF7; // Bit 4 is set, so clear it
00237             } else {
00238                 CRC = CRC | 0x08; // Bit 4 is clear, so set it
00239             }
00240         } else {
00241             // DATA ^ LSB CRC = 0
00242             CRC = CRC>>1;
00243             // clear MSB
00244             CRC = CRC & 0x7F;
00245             // No need to check bits, with DATA ^ LSB CRC = 0, they will remain unchanged
00246         }
00247         byte = byte>>1;
00248     }
00249 return CRC;
00250 }
00251  
00252 int DS1820::convert_temperature(bool wait, devices device) {
00253     // Convert temperature into scratchpad RAM for all devices at once
00254     int delay_time = 750; // Default delay time
00255     char resolution;
00256     if (device==all_devices)
00257         skip_ROM();          // Skip ROM command, will convert for ALL devices
00258     else {
00259         match_ROM();
00260         if (FAMILY_CODE == FAMILY_CODE_DS18B20 ) {
00261             resolution = RAM[4] & 0x60;
00262             if (resolution == 0x00) // 9 bits
00263                 delay_time = 94;
00264             if (resolution == 0x20) // 10 bits
00265                 delay_time = 188;
00266             if (resolution == 0x40) // 11 bits. Note 12bits uses the 750ms default
00267                 delay_time = 375;
00268         }
00269     }
00270     onewire_byte_out( 0x44);  // perform temperature conversion
00271     if (_parasite_power) {
00272         _parasitepin = 1;     // Parasite power strong pullup
00273         wait_ms(delay_time);
00274         _parasitepin = 0;
00275         delay_time = 0;
00276     } else {
00277         if (wait) {
00278             wait_ms(delay_time);
00279             delay_time = 0;
00280         }
00281     }
00282     return delay_time;
00283 }
00284  
00285 void DS1820::read_RAM() {
00286     // This will copy the DS1820's 9 bytes of RAM data
00287     // into the objects RAM array. Functions that use
00288     // RAM values will automaticly call this procedure.
00289     int i;
00290     match_ROM();             // Select this device
00291     onewire_byte_out( 0xBE);   //Read Scratchpad command
00292     for(i=0;i<9;i++) {
00293         RAM[i] = onewire_byte_in();
00294     }
00295 //    if (!RAM_checksum_error())
00296 //       crcerr = 1;
00297 }
00298 
00299 bool DS1820::set_configuration_bits(unsigned int resolution) {
00300     bool answer = false;
00301     resolution = resolution - 9;
00302     if (resolution < 4) {
00303         resolution = resolution<<5; // align the bits
00304         RAM[4] = (RAM[4] & 0x60) | resolution; // mask out old data, insert new
00305         write_scratchpad ((RAM[2]<<8) + RAM[3]);
00306 //        store_scratchpad (DS1820::this_device); // Need to test if this is required
00307         answer = true;
00308     }
00309     return answer;
00310 }
00311  
00312 int DS1820::read_scratchpad() {
00313     int answer;
00314     read_RAM();
00315     answer = (RAM[2]<<8) + RAM[3];
00316     return answer;
00317 }
00318  
00319 void DS1820::write_scratchpad(int data) {
00320     RAM[3] = data;
00321     RAM[2] = data>>8;
00322     match_ROM();
00323     onewire_byte_out(0x4E);   // Copy scratchpad into DS1820 ram memory
00324     onewire_byte_out(RAM[2]); // T(H)
00325     onewire_byte_out(RAM[3]); // T(L)
00326     if ( FAMILY_CODE == FAMILY_CODE_DS18B20 ) {
00327         onewire_byte_out(RAM[4]); // Configuration register
00328     }
00329 }
00330  
00331 void DS1820::store_scratchpad(devices device) {
00332     if (device==all_devices)
00333         skip_ROM();          // Skip ROM command, will store for ALL devices
00334     else
00335         match_ROM();
00336     onewire_byte_out(0x48);   // Write scratchpad into E2 command
00337     if (_parasite_power)
00338         _parasitepin=1;
00339     wait_ms(10);            // Parasite power strong pullup for 10ms
00340     if (_parasite_power)
00341         _parasitepin=0;
00342 }
00343  
00344 int DS1820::recall_scratchpad(devices device) {
00345 // This copies the E2 values into the DS1820's memory.
00346 // If you specify all_devices this will return zero, otherwise
00347 // it will return the value of the scratchpad memory.
00348     int answer=0;
00349     if (device==all_devices)
00350         skip_ROM();          // Skip ROM command, will recall for ALL devices
00351     else
00352         match_ROM();
00353     onewire_byte_out(0xB8);   // Recall E2 data to scratchpad command
00354     wait_ms(10); // not sure I like polling for completion
00355                  // it could cause an infinite loop
00356     if (device==DS1820::this_device) {
00357         read_RAM();
00358         answer = read_scratchpad();
00359     }
00360     return answer;
00361 }    
00362  
00363 float DS1820::temperature(char scale) {
00364 // The data specs state that count_per_degree should be 0x10 (16), I found my devices
00365 // to have a count_per_degree of 0x4B (75). With the standard resolution of 1/2 deg C
00366 // this allowed an expanded resolution of 1/150th of a deg C. I wouldn't rely on this
00367 // being super acurate, but it does allow for a smooth display in the 1/10ths of a
00368 // deg C or F scales.
00369     float answer, remaining_count, count_per_degree;
00370     int reading;
00371     read_RAM();
00372     if (RAM_checksum_error())
00373         // Indicate we got a CRC error
00374         answer = -1000.0;
00375     else {
00376         reading = (RAM[1] << 8) + RAM[0];
00377         if (reading & 0x8000) { // negative degrees C
00378             reading = 0-((reading ^ 0xffff) + 1); // 2's comp then convert to signed int
00379         }
00380         answer = reading +0.0; // convert to floating point
00381         if ( FAMILY_CODE == FAMILY_CODE_DS18B20 ) {
00382             answer = answer / 8.0;
00383         }
00384         else {
00385             remaining_count = RAM[6];
00386             count_per_degree = RAM[7];
00387             answer = answer - 0.25 + (count_per_degree - remaining_count) / count_per_degree;
00388         }
00389         if (scale=='C' or scale=='c')
00390             answer = answer / 2.0;
00391         else
00392             // Convert to deg F
00393             answer = answer * 9.0 / 10.0 + 32.0;
00394     }
00395     return answer;
00396 }
00397  
00398 bool DS1820::read_power_supply(devices device) {
00399 // This will return true if the device (or all devices) are Vcc powered
00400 // This will return false if the device (or ANY device) is parasite powered
00401     if (device==all_devices)
00402         skip_ROM();          // Skip ROM command, will poll for any device using parasite power
00403     else
00404         match_ROM();
00405     onewire_byte_out(0xB4);   // Read power supply command
00406     return onewire_bit_in();
00407 }
00408 
00409