Kernel driver pca9539
=====================

Supported chips:
  * Philips PCA9539
    Prefix: 'pca9539'
    Addresses scanned: 0x74 - 0x77
    Datasheet:
        http://www.semiconductors.philips.com/acrobat/datasheets/PCA9539_2.pdf

Author: Ben Gardner <bgardner@wabtec.com>


Description
-----------

The Philips PCA9539 is a 16 bit low power I/O device.
All 16 lines can be individually configured as an input or output.
The input sense can also be inverted.
The 16 lines are split between two bytes.


Sysfs entries
-------------

Each is a byte that maps to the 8 I/O bits.
A '0' suffix is for bits 0-7, while '1' is for bits 8-15.

input[01]     - read the current value
output[01]    - sets the output value
direction[01] - direction of each bit: 1=input, 0=output
invert[01]    - toggle the input bit sense

input reads the actual state of the line and is always available.
The direction defaults to input for all channels.


General Remarks
---------------

Note that each output, direction, and invert entry controls 8 lines.
You should use the read, modify, write sequence.
For example. to set output bit 0 of 1.
  val=$(cat output0)
  val=$(( $val | 1 ))
  echo $val > output0

