1Kernel driver ds1621 2==================== 3 4Supported chips: 5 6 * Dallas Semiconductor / Maxim Integrated DS1621 7 8 Prefix: 'ds1621' 9 10 Addresses scanned: none 11 12 Datasheet: Publicly available from www.maximintegrated.com 13 14 * Dallas Semiconductor DS1625 15 16 Prefix: 'ds1625' 17 18 Addresses scanned: none 19 20 Datasheet: Publicly available from www.datasheetarchive.com 21 22 * Maxim Integrated DS1631 23 24 Prefix: 'ds1631' 25 26 Addresses scanned: none 27 28 Datasheet: Publicly available from www.maximintegrated.com 29 30 * Maxim Integrated DS1721 31 32 Prefix: 'ds1721' 33 34 Addresses scanned: none 35 36 Datasheet: Publicly available from www.maximintegrated.com 37 38 * Maxim Integrated DS1731 39 40 Prefix: 'ds1731' 41 42 Addresses scanned: none 43 44 Datasheet: Publicly available from www.maximintegrated.com 45 46Authors: 47 - Christian W. Zuckschwerdt <zany@triq.net> 48 - valuable contributions by Jan M. Sendler <sendler@sendler.de> 49 - ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net> 50 with the help of Jean Delvare <jdelvare@suse.de> 51 52Module Parameters 53------------------ 54 55* polarity int 56 Output's polarity: 57 58 * 0 = active high, 59 * 1 = active low 60 61Description 62----------- 63 64The DS1621 is a (one instance) digital thermometer and thermostat. It has 65both high and low temperature limits which can be user defined (i.e. 66programmed into non-volatile on-chip registers). Temperature range is -55 67degree Celsius to +125 in 0.5 increments. You may convert this into a 68Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity 69parameter is not provided, original value is used. 70 71As for the thermostat, behavior can also be programmed using the polarity 72toggle. On the one hand ("heater"), the thermostat output of the chip, 73Tout, will trigger when the low limit temperature is met or underrun and 74stays high until the high limit is met or exceeded. On the other hand 75("cooler"), vice versa. That way "heater" equals "active low", whereas 76"conditioner" equals "active high". Please note that the DS1621 data sheet 77is somewhat misleading in this point since setting the polarity bit does 78not simply invert Tout. 79 80A second thing is that, during extensive testing, Tout showed a tolerance 81of up to +/- 0.5 degrees even when compared against precise temperature 82readings. Be sure to have a high vs. low temperature limit gap of al least 831.0 degree Celsius to avoid Tout "bouncing", though! 84 85The alarm bits are set when the high or low limits are met or exceeded and 86are reset by the module as soon as the respective temperature ranges are 87left. 88 89The alarm registers are in no way suitable to find out about the actual 90status of Tout. They will only tell you about its history, whether or not 91any of the limits have ever been met or exceeded since last power-up or 92reset. Be aware: When testing, it showed that the status of Tout can change 93with neither of the alarms set. 94 95Since there is no version or vendor identification register, there is 96no unique identification for these devices. Therefore, explicit device 97instantiation is required for correct device identification and functionality 98(one device per address in this address range: 0x48..0x4f). 99 100The DS1625 is pin compatible and functionally equivalent with the DS1621, 101but the DS1621 is meant to replace it. The DS1631, DS1721, and DS1731 are 102also pin compatible with the DS1621 and provide multi-resolution support. 103 104Additionally, the DS1721 data sheet says the temperature flags (THF and TLF) 105are used internally, however, these flags do get set and cleared as the actual 106temperature crosses the min or max settings (which by default are set to 75 107and 80 degrees respectively). 108 109Temperature Conversion 110---------------------- 111 112- DS1621 - 750ms (older devices may take up to 1000ms) 113- DS1625 - 500ms 114- DS1631 - 93ms..750ms for 9..12 bits resolution, respectively. 115- DS1721 - 93ms..750ms for 9..12 bits resolution, respectively. 116- DS1731 - 93ms..750ms for 9..12 bits resolution, respectively. 117 118Note: 119On the DS1621, internal access to non-volatile registers may last for 10ms 120or less (unverified on the other devices). 121 122Temperature Accuracy 123-------------------- 124 125- DS1621: +/- 0.5 degree Celsius (from 0 to +70 degrees) 126- DS1625: +/- 0.5 degree Celsius (from 0 to +70 degrees) 127- DS1631: +/- 0.5 degree Celsius (from 0 to +70 degrees) 128- DS1721: +/- 1.0 degree Celsius (from -10 to +85 degrees) 129- DS1731: +/- 1.0 degree Celsius (from -10 to +85 degrees) 130 131.. Note:: 132 133 Please refer to the device datasheets for accuracy at other temperatures. 134 135Temperature Resolution: 136----------------------- 137As mentioned above, the DS1631, DS1721, and DS1731 provide multi-resolution 138support, which is achieved via the R0 and R1 config register bits, where: 139 140R0..R1 141------ 142 143== == =============================== 144R0 R1 145== == =============================== 146 0 0 9 bits, 0.5 degrees Celsius 147 1 0 10 bits, 0.25 degrees Celsius 148 0 1 11 bits, 0.125 degrees Celsius 149 1 1 12 bits, 0.0625 degrees Celsius 150== == =============================== 151 152.. Note:: 153 154 At initial device power-on, the default resolution is set to 12-bits. 155 156The resolution mode for the DS1631, DS1721, or DS1731 can be changed from 157userspace, via the device 'update_interval' sysfs attribute. This attribute 158will normalize the range of input values to the device maximum resolution 159values defined in the datasheet as follows: 160 161============= ================== =============== 162Resolution Conversion Time Input Range 163 (C/LSB) (msec) (msec) 164============= ================== =============== 1650.5 93.75 0....94 1660.25 187.5 95...187 1670.125 375 188..375 1680.0625 750 376..infinity 169============= ================== =============== 170 171The following examples show how the 'update_interval' attribute can be 172used to change the conversion time:: 173 174 $ cat update_interval 175 750 176 $ cat temp1_input 177 22062 178 $ 179 $ echo 300 > update_interval 180 $ cat update_interval 181 375 182 $ cat temp1_input 183 22125 184 $ 185 $ echo 150 > update_interval 186 $ cat update_interval 187 188 188 $ cat temp1_input 189 22250 190 $ 191 $ echo 1 > update_interval 192 $ cat update_interval 193 94 194 $ cat temp1_input 195 22000 196 $ 197 $ echo 1000 > update_interval 198 $ cat update_interval 199 750 200 $ cat temp1_input 201 22062 202 $ 203 204As shown, the ds1621 driver automatically adjusts the 'update_interval' 205user input, via a step function. Reading back the 'update_interval' value 206after a write operation provides the conversion time used by the device. 207 208Mathematically, the resolution can be derived from the conversion time 209via the following function: 210 211 g(x) = 0.5 * [minimum_conversion_time/x] 212 213where: 214 215 - 'x' = the output from 'update_interval' 216 - 'g(x)' = the resolution in degrees C per LSB. 217 - 93.75ms = minimum conversion time 218