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