linux/Documentation/misc-devices/ad525x_dpot.txt
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   1---------------------------------
   2  AD525x Digital Potentiometers
   3---------------------------------
   4
   5The ad525x_dpot driver exports a simple sysfs interface.  This allows you to
   6work with the immediate resistance settings as well as update the saved startup
   7settings.  Access to the factory programmed tolerance is also provided, but
   8interpretation of this settings is required by the end application according to
   9the specific part in use.
  10
  11---------
  12  Files
  13---------
  14
  15Each dpot device will have a set of eeprom, rdac, and tolerance files.  How
  16many depends on the actual part you have, as will the range of allowed values.
  17
  18The eeprom files are used to program the startup value of the device.
  19
  20The rdac files are used to program the immediate value of the device.
  21
  22The tolerance files are the read-only factory programmed tolerance settings
  23and may vary greatly on a part-by-part basis.  For exact interpretation of
  24this field, please consult the datasheet for your part.  This is presented
  25as a hex file for easier parsing.
  26
  27-----------
  28  Example
  29-----------
  30
  31Locate the device in your sysfs tree.  This is probably easiest by going into
  32the common i2c directory and locating the device by the i2c slave address.
  33
  34        # ls /sys/bus/i2c/devices/
  35        0-0022  0-0027  0-002f
  36
  37So assuming the device in question is on the first i2c bus and has the slave
  38address of 0x2f, we descend (unrelated sysfs entries have been trimmed).
  39
  40        # ls /sys/bus/i2c/devices/0-002f/
  41        eeprom0 rdac0 tolerance0
  42
  43You can use simple reads/writes to access these files:
  44
  45        # cd /sys/bus/i2c/devices/0-002f/
  46
  47        # cat eeprom0
  48        0
  49        # echo 10 > eeprom0
  50        # cat eeprom0
  51        10
  52
  53        # cat rdac0
  54        5
  55        # echo 3 > rdac0
  56        # cat rdac0
  57        3
  58
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