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Diffstat (limited to 'Documentation/hwmon/max31827.rst')
| -rw-r--r-- | Documentation/hwmon/max31827.rst | 75 |
1 files changed, 61 insertions, 14 deletions
diff --git a/Documentation/hwmon/max31827.rst b/Documentation/hwmon/max31827.rst index 9a1055a007..44ab9dc064 100644 --- a/Documentation/hwmon/max31827.rst +++ b/Documentation/hwmon/max31827.rst @@ -52,13 +52,21 @@ MAX31827 has low and over temperature alarms with an effective value and a hysteresis value: -40 and -30 degrees for under temperature alarm and +100 and +90 degrees for over temperature alarm. -The alarm can be configured in comparator and interrupt mode. Currently only -comparator mode is implemented. In Comparator mode, the OT/UT status bits have a -value of 1 when the temperature rises above the TH value or falls below TL, -which is also subject to the Fault Queue selection. OT status returns to 0 when -the temperature drops below the TH_HYST value or when shutdown mode is entered. -Similarly, UT status returns to 0 when the temperature rises above TL_HYST value -or when shutdown mode is entered. +The alarm can be configured in comparator and interrupt mode from the +devicetree. In Comparator mode, the OT/UT status bits have a value of 1 when the +temperature rises above the TH value or falls below TL, which is also subject to +the Fault Queue selection. OT status returns to 0 when the temperature drops +below the TH_HYST value or when shutdown mode is entered. Similarly, UT status +returns to 0 when the temperature rises above TL_HYST value or when shutdown +mode is entered. + +In interrupt mode exceeding TH also sets OT status to 1, which remains set until +a read operation is performed on the configuration/status register (max or min +attribute); at this point, it returns to 0. Once OT status is set to 1 from +exceeding TH and reset, it is set to 1 again only when the temperature drops +below TH_HYST. The output remains asserted until it is reset by a read. It is +set again if the temperature rises above TH, and so on. The same logic applies +to the operation of the UT status bit. Putting the MAX31827 into shutdown mode also resets the OT/UT status bits. Note that if the mode is changed while OT/UT status bits are set, an OT/UT status @@ -68,13 +76,42 @@ clear the status bits before changing the operating mode. The conversions can be manual with the one-shot functionality and automatic with a set frequency. When powered on, the chip measures temperatures with 1 conv/s. +The conversion rate can be modified with update_interval attribute of the chip. +Conversion/second = 1/update_interval. Thus, the available options according to +the data sheet are: + +- 64000 (ms) = 1 conv/64 sec +- 32000 (ms) = 1 conv/32 sec +- 16000 (ms) = 1 conv/16 sec +- 4000 (ms) = 1 conv/4 sec +- 1000 (ms) = 1 conv/sec (default) +- 250 (ms) = 4 conv/sec +- 125 (ms) = 8 conv/sec + Enabling the device when it is already enabled has the side effect of setting the conversion frequency to 1 conv/s. The conversion time varies depending on -the resolution. The conversion time doubles with every bit of increased -resolution. For 10 bit resolution 35ms are needed, while for 12 bit resolution -(default) 140ms. When chip is in shutdown mode and a read operation is -requested, one-shot is triggered, the device waits for 140 (conversion time) ms, -and only after that is the temperature value register read. +the resolution. + +The conversion time doubles with every bit of increased resolution. The +available resolutions are: + +- 8 bit -> 8.75 ms conversion time +- 9 bit -> 17.5 ms conversion time +- 10 bit -> 35 ms conversion time +- 12 bit (default) -> 140 ms conversion time + +There is a temp1_resolution attribute which indicates the unit change in the +input temperature in milli-degrees C. + +- 1000 mC -> 8 bit +- 500 mC -> 9 bit +- 250 mC -> 10 bit +- 62 mC -> 12 bit (default) - actually this is 62.5, but the fil returns 62 + +When chip is in shutdown mode and a read operation is requested, one-shot is +triggered, the device waits for <conversion time> ms, and only after that is +the temperature value register read. Note that the conversion times are rounded +up to the nearest possible integer. The LSB of the temperature values is 0.0625 degrees Celsius, but the values of the temperatures are displayed in milli-degrees. This means, that some data is @@ -83,8 +120,18 @@ in the writing of alarm values too. For positive numbers the user-input value will always be rounded down to the nearest possible value, for negative numbers the user-input will always be rounded up to the nearest possible value. +Bus timeout resets the I2C-compatible interface when SCL is low for more than +30ms (nominal). + +Alarm polarity determines if the active state of the alarm is low or high. The +behavior for both settings is dependent on the Fault Queue setting. The ALARM +pin is an open-drain output and requires a pullup resistor to operate. + +The Fault Queue bits select how many consecutive temperature faults must occur +before overtemperature or undertemperature faults are indicated in the +corresponding status bits. + Notes ----- -Currently fault queue, alarm polarity and resolution cannot be modified. -PEC is not implemented either. +PEC is not implemented. |