diff options
Diffstat (limited to 'Documentation/w1/slaves/w1_ds2438.rst')
| -rw-r--r-- | Documentation/w1/slaves/w1_ds2438.rst | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/Documentation/w1/slaves/w1_ds2438.rst b/Documentation/w1/slaves/w1_ds2438.rst new file mode 100644 index 000000000..4fa671fbc --- /dev/null +++ b/Documentation/w1/slaves/w1_ds2438.rst @@ -0,0 +1,86 @@ +Kernel driver w1_ds2438 +======================= + +Supported chips: + + * Maxim DS2438 Smart Battery Monitor + +supported family codes: + ================ ==== + W1_FAMILY_DS2438 0x26 + ================ ==== + +Author: Mariusz Bialonczyk <manio@skyboo.net> + +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. |