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86 lines
3.0 KiB
86 lines
3.0 KiB
Kernel driver w1_ds2438 |
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======================= |
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Supported chips: |
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* Maxim DS2438 Smart Battery Monitor |
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supported family codes: |
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================ ==== |
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W1_FAMILY_DS2438 0x26 |
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================ ==== |
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Author: Mariusz Bialonczyk <[email protected]> |
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Description |
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----------- |
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The DS2438 chip provides several functions that are desirable to carry in |
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a battery pack. It also has a 40 bytes of nonvolatile EEPROM. |
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Because the ability of temperature, current and voltage measurement, the chip |
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is also often used in weather stations and applications such as: rain gauge, |
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wind speed/direction measuring, humidity sensing, etc. |
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Current support is provided through the following sysfs files (all files |
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except "iad" and "offset" are readonly): |
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"iad" |
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----- |
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This file controls the 'Current A/D Control Bit' (IAD) in the |
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Status/Configuration Register. |
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Writing a zero value will clear the IAD bit and disables the current |
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measurements. |
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Writing value "1" is setting the IAD bit (enables the measurements). |
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The IAD bit is enabled by default in the DS2438. |
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When writing to sysfs file bits 2-7 are ignored, so it's safe to write ASCII. |
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An I/O error is returned when there is a problem setting the new value. |
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"page0" |
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------- |
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This file provides full 8 bytes of the chip Page 0 (00h). |
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This page contains the most frequently accessed information of the DS2438. |
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Internally when this file is read, the additional CRC byte is also obtained |
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from the slave device. If it is correct, the 8 bytes page data are passed |
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to userspace, otherwise an I/O error is returned. |
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"page1" |
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------- |
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This file provides full 8 bytes of the chip Page 1 (01h). |
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This page contains the ICA, elapsed time meter and current offset data of the DS2438. |
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Internally when this file is read, the additional CRC byte is also obtained |
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from the slave device. If it is correct, the 8 bytes page data are passed |
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to userspace, otherwise an I/O error is returned. |
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"offset" |
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-------- |
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This file controls the 2-byte Offset Register of the chip. |
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Writing a 2-byte value will change the Offset Register, which changes the |
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current measurement done by the chip. Changing this register to the two's complement |
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of the current register while forcing zero current through the load will calibrate |
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the chip, canceling offset errors in the current ADC. |
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"temperature" |
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------------- |
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Opening and reading this file initiates the CONVERT_T (temperature conversion) |
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command of the chip, afterwards the temperature is read from the device |
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registers and provided as an ASCII decimal value. |
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Important: The returned value has to be divided by 256 to get a real |
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temperature in degrees Celsius. |
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"vad", "vdd" |
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------------ |
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Opening and reading this file initiates the CONVERT_V (voltage conversion) |
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command of the chip. |
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Depending on a sysfs filename a different input for the A/D will be selected: |
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vad: |
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general purpose A/D input (VAD) |
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vdd: |
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battery input (VDD) |
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After the voltage conversion the value is returned as decimal ASCII. |
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Note: To get a volts the value has to be divided by 100.
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