LXR linux/Documentation/hwmon/pcf8591.rst

   1Kernel driver pcf8591
   2=====================
   3
   4Supported chips:
   5
   6  * Philips/NXP PCF8591
   7
   8    Prefix: 'pcf8591'
   9
  10    Addresses scanned: none
  11
  12    Datasheet: Publicly available at the NXP website
  13
  14               http://www.nxp.com/pip/PCF8591_6.html
  15
  16Authors:
  17      - Aurelien Jarno <aurelien@aurel32.net>
  18      - valuable contributions by Jan M. Sendler <sendler@sendler.de>,
  19      - Jean Delvare <jdelvare@suse.de>
  20
  21
  22Description
  23-----------
  24
  25The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one
  26analog output) for the I2C bus produced by Philips Semiconductors (now NXP).
  27It is designed to provide a byte I2C interface to up to 4 separate devices.
  28
  29The PCF8591 has 4 analog inputs programmable as single-ended or
  30differential inputs:
  31
  32- mode 0 : four single ended inputs
  33        Pins AIN0 to AIN3 are single ended inputs for channels 0 to 3
  34
  35- mode 1 : three differential inputs
  36        Pins AIN3 is the common negative differential input
  37        Pins AIN0 to AIN2 are positive differential inputs for channels 0 to 2
  38
  39- mode 2 : single ended and differential mixed
  40        Pins AIN0 and AIN1 are single ended inputs for channels 0 and 1
  41        Pins AIN2 is the positive differential input for channel 3
  42        Pins AIN3 is the negative differential input for channel 3
  43
  44- mode 3 : two differential inputs
  45        Pins AIN0 is the positive differential input for channel 0
  46        Pins AIN1 is the negative differential input for channel 0
  47        Pins AIN2 is the positive differential input for channel 1
  48        Pins AIN3 is the negative differential input for channel 1
  49
  50See the datasheet for details.
  51
  52Module parameters
  53-----------------
  54
  55* input_mode int
  56
  57    Analog input mode:
  58
  59         - 0 = four single ended inputs
  60         - 1 = three differential inputs
  61         - 2 = single ended and differential mixed
  62         - 3 = two differential inputs
  63
  64
  65Accessing PCF8591 via /sys interface
  66-------------------------------------
  67
  68The PCF8591 is plainly impossible to detect! Thus the driver won't even
  69try. You have to explicitly instantiate the device at the relevant
  70address (in the interval [0x48..0x4f]) either through platform data, or
  71using the sysfs interface. See Documentation/i2c/instantiating-devices.rst
  72for details.
  73
  74Directories are being created for each instantiated PCF8591:
  75
  76/sys/bus/i2c/devices/<0>-<1>/
  77   where <0> is the bus the chip is connected to (e. g. i2c-0)
  78   and <1> the chip address ([48..4f])
  79
  80Inside these directories, there are such files:
  81
  82   in0_input, in1_input, in2_input, in3_input, out0_enable, out0_output, name
  83
  84Name contains chip name.
  85
  86The in0_input, in1_input, in2_input and in3_input files are RO. Reading gives
  87the value of the corresponding channel. Depending on the current analog inputs
  88configuration, files in2_input and in3_input may not exist. Values range
  89from 0 to 255 for single ended inputs and -128 to +127 for differential inputs
  90(8-bit ADC).
  91
  92The out0_enable file is RW. Reading gives "1" for analog output enabled and
  93"0" for analog output disabled. Writing accepts "0" and "1" accordingly.
  94
  95The out0_output file is RW. Writing a number between 0 and 255 (8-bit DAC), send
  96the value to the digital-to-analog converter. Note that a voltage will
  97only appears on AOUT pin if aout0_enable equals 1. Reading returns the last
  98value written.
  99