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217 lines
6.7 KiB
217 lines
6.7 KiB
Kernel driver ds1621 |
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==================== |
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Supported chips: |
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* Dallas Semiconductor / Maxim Integrated DS1621 |
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Prefix: 'ds1621' |
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Addresses scanned: none |
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Datasheet: Publicly available from www.maximintegrated.com |
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* Dallas Semiconductor DS1625 |
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Prefix: 'ds1625' |
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Addresses scanned: none |
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Datasheet: Publicly available from www.datasheetarchive.com |
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* Maxim Integrated DS1631 |
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Prefix: 'ds1631' |
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Addresses scanned: none |
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Datasheet: Publicly available from www.maximintegrated.com |
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* Maxim Integrated DS1721 |
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Prefix: 'ds1721' |
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Addresses scanned: none |
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Datasheet: Publicly available from www.maximintegrated.com |
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* Maxim Integrated DS1731 |
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Prefix: 'ds1731' |
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Addresses scanned: none |
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Datasheet: Publicly available from www.maximintegrated.com |
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Authors: |
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- Christian W. Zuckschwerdt <[email protected]> |
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- valuable contributions by Jan M. Sendler <[email protected]> |
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- ported to 2.6 by Aurelien Jarno <[email protected]> |
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with the help of Jean Delvare <[email protected]> |
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Module Parameters |
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------------------ |
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* polarity int |
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Output's polarity: |
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* 0 = active high, |
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* 1 = active low |
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Description |
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----------- |
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The DS1621 is a (one instance) digital thermometer and thermostat. It has |
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both high and low temperature limits which can be user defined (i.e. |
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programmed into non-volatile on-chip registers). Temperature range is -55 |
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degree Celsius to +125 in 0.5 increments. You may convert this into a |
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Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity |
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parameter is not provided, original value is used. |
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As for the thermostat, behavior can also be programmed using the polarity |
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toggle. On the one hand ("heater"), the thermostat output of the chip, |
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Tout, will trigger when the low limit temperature is met or underrun and |
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stays high until the high limit is met or exceeded. On the other hand |
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("cooler"), vice versa. That way "heater" equals "active low", whereas |
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"conditioner" equals "active high". Please note that the DS1621 data sheet |
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is somewhat misleading in this point since setting the polarity bit does |
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not simply invert Tout. |
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A second thing is that, during extensive testing, Tout showed a tolerance |
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of up to +/- 0.5 degrees even when compared against precise temperature |
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readings. Be sure to have a high vs. low temperature limit gap of al least |
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1.0 degree Celsius to avoid Tout "bouncing", though! |
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The alarm bits are set when the high or low limits are met or exceeded and |
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are reset by the module as soon as the respective temperature ranges are |
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left. |
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The alarm registers are in no way suitable to find out about the actual |
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status of Tout. They will only tell you about its history, whether or not |
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any of the limits have ever been met or exceeded since last power-up or |
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reset. Be aware: When testing, it showed that the status of Tout can change |
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with neither of the alarms set. |
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Since there is no version or vendor identification register, there is |
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no unique identification for these devices. Therefore, explicit device |
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instantiation is required for correct device identification and functionality |
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(one device per address in this address range: 0x48..0x4f). |
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The DS1625 is pin compatible and functionally equivalent with the DS1621, |
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but the DS1621 is meant to replace it. The DS1631, DS1721, and DS1731 are |
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also pin compatible with the DS1621 and provide multi-resolution support. |
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Additionally, the DS1721 data sheet says the temperature flags (THF and TLF) |
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are used internally, however, these flags do get set and cleared as the actual |
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temperature crosses the min or max settings (which by default are set to 75 |
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and 80 degrees respectively). |
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Temperature Conversion |
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---------------------- |
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- DS1621 - 750ms (older devices may take up to 1000ms) |
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- DS1625 - 500ms |
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- DS1631 - 93ms..750ms for 9..12 bits resolution, respectively. |
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- DS1721 - 93ms..750ms for 9..12 bits resolution, respectively. |
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- DS1731 - 93ms..750ms for 9..12 bits resolution, respectively. |
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Note: |
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On the DS1621, internal access to non-volatile registers may last for 10ms |
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or less (unverified on the other devices). |
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Temperature Accuracy |
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-------------------- |
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- DS1621: +/- 0.5 degree Celsius (from 0 to +70 degrees) |
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- DS1625: +/- 0.5 degree Celsius (from 0 to +70 degrees) |
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- DS1631: +/- 0.5 degree Celsius (from 0 to +70 degrees) |
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- DS1721: +/- 1.0 degree Celsius (from -10 to +85 degrees) |
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- DS1731: +/- 1.0 degree Celsius (from -10 to +85 degrees) |
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.. Note:: |
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Please refer to the device datasheets for accuracy at other temperatures. |
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Temperature Resolution: |
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----------------------- |
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As mentioned above, the DS1631, DS1721, and DS1731 provide multi-resolution |
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support, which is achieved via the R0 and R1 config register bits, where: |
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R0..R1 |
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------ |
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== == =============================== |
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R0 R1 |
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== == =============================== |
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0 0 9 bits, 0.5 degrees Celsius |
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1 0 10 bits, 0.25 degrees Celsius |
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0 1 11 bits, 0.125 degrees Celsius |
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1 1 12 bits, 0.0625 degrees Celsius |
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== == =============================== |
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.. Note:: |
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At initial device power-on, the default resolution is set to 12-bits. |
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The resolution mode for the DS1631, DS1721, or DS1731 can be changed from |
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userspace, via the device 'update_interval' sysfs attribute. This attribute |
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will normalize the range of input values to the device maximum resolution |
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values defined in the datasheet as follows: |
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============= ================== =============== |
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Resolution Conversion Time Input Range |
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(C/LSB) (msec) (msec) |
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============= ================== =============== |
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0.5 93.75 0....94 |
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0.25 187.5 95...187 |
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0.125 375 188..375 |
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0.0625 750 376..infinity |
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============= ================== =============== |
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The following examples show how the 'update_interval' attribute can be |
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used to change the conversion time:: |
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$ cat update_interval |
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750 |
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$ cat temp1_input |
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22062 |
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$ |
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$ echo 300 > update_interval |
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$ cat update_interval |
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375 |
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$ cat temp1_input |
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22125 |
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$ |
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$ echo 150 > update_interval |
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$ cat update_interval |
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188 |
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$ cat temp1_input |
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22250 |
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$ |
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$ echo 1 > update_interval |
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$ cat update_interval |
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94 |
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$ cat temp1_input |
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22000 |
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$ |
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$ echo 1000 > update_interval |
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$ cat update_interval |
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750 |
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$ cat temp1_input |
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22062 |
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$ |
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As shown, the ds1621 driver automatically adjusts the 'update_interval' |
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user input, via a step function. Reading back the 'update_interval' value |
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after a write operation provides the conversion time used by the device. |
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Mathematically, the resolution can be derived from the conversion time |
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via the following function: |
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g(x) = 0.5 * [minimum_conversion_time/x] |
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where: |
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- 'x' = the output from 'update_interval' |
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- 'g(x)' = the resolution in degrees C per LSB. |
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- 93.75ms = minimum conversion time
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