Kernel driver pcf8591
  =====================
  
  Supported chips:

    * Philips/NXP PCF8591

      Prefix: 'pcf8591'

      Addresses scanned: none

      Datasheet: Publicly available at the NXP website
                 http://www.nxp.com/pip/PCF8591_6.html

  
  Authors:
          Aurelien Jarno <aurelien@aurel32.net>
          valuable contributions by Jan M. Sendler <sendler@sendler.de>,
          Jean Delvare <khali@linux-fr.org>
  
  
  Description
  -----------

  The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one

  analog output) for the I2C bus produced by Philips Semiconductors (now NXP).
  It is designed to provide a byte I2C interface to up to 4 separate devices.

  
  The PCF8591 has 4 analog inputs programmable as single-ended or
  differential inputs :
  - mode 0 : four single ended inputs
          Pins AIN0 to AIN3 are single ended inputs for channels 0 to 3
  
  - mode 1 : three differential inputs
          Pins AIN3 is the common negative differential input
          Pins AIN0 to AIN2 are positive differential inputs for channels 0 to 2
  
  - mode 2 : single ended and differential mixed
          Pins AIN0 and AIN1 are single ended inputs for channels 0 and 1
          Pins AIN2 is the positive differential input for channel 3
          Pins AIN3 is the negative differential input for channel 3
  
  - mode 3 : two differential inputs
          Pins AIN0 is the positive differential input for channel 0
          Pins AIN1 is the negative differential input for channel 0
          Pins AIN2 is the positive differential input for channel 1
          Pins AIN3 is the negative differential input for channel 1
  
  See the datasheet for details.
  
  Module parameters
  -----------------
  
  * input_mode int
  
      Analog input mode:
           0 = four single ended inputs
           1 = three differential inputs
           2 = single ended and differential mixed
           3 = two differential inputs
  
  
  Accessing PCF8591 via /sys interface
  -------------------------------------

  The PCF8591 is plainly impossible to detect! Thus the driver won't even
  try. You have to explicitly instantiate the device at the relevant
  address (in the interval [0x48..0x4f]) either through platform data, or
  using the sysfs interface. See Documentation/i2c/instantiating-devices
  for details.

  Directories are being created for each instantiated PCF8591:

  /sys/bus/i2c/devices/<0>-<1>/

  where <0> is the bus the chip is connected to (e. g. i2c-0)

  and <1> the chip address ([48..4f])
  
  Inside these directories, there are such files:

  in0_input, in1_input, in2_input, in3_input, out0_enable, out0_output, name

  
  Name contains chip name.

  The in0_input, in1_input, in2_input and in3_input files are RO. Reading gives
  the value of the corresponding channel. Depending on the current analog inputs
  configuration, files in2_input and in3_input may not exist. Values range
  from 0 to 255 for single ended inputs and -128 to +127 for differential inputs
  (8-bit ADC).

  
  The out0_enable file is RW. Reading gives "1" for analog output enabled and
  "0" for analog output disabled. Writing accepts "0" and "1" accordingly.
  
  The out0_output file is RW. Writing a number between 0 and 255 (8-bit DAC), send
  the value to the digital-to-analog converter. Note that a voltage will
  only appears on AOUT pin if aout0_enable equals 1. Reading returns the last
  value written.