Documentation/hwmon/pcf8591

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