Kernel driver w1_ds2413
=======================

Supported chips:
  * Maxim DS2413 1-Wire Dual Channel Addressable Switch

supported family codes:
        W1_FAMILY_DS2413        0x3A

Author: Mariusz Bialonczyk <manio@skyboo.net>

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

The DS2413 chip has two open-drain outputs (PIO A and PIO B).
Support is provided through the sysfs files "output" and "state".

Reading state
-------------
The "state" file provides one-byte value which is in the same format as for
the chip PIO_ACCESS_READ command (refer the datasheet for details):

Bit 0:   PIOA Pin State
Bit 1:   PIOA Output Latch State
Bit 2:   PIOB Pin State
Bit 3:   PIOB Output Latch State
Bit 4-7: Complement of Bit 3 to Bit 0 (verified by the kernel module)

This file is readonly.

Writing output
--------------
You can set the PIO pins using the "output" file.
It is writable, you can write one-byte value to this sysfs file.
Similarly the byte format is the same as for the PIO_ACCESS_WRITE command:

Bit 0:   PIOA
Bit 1:   PIOB
Bit 2-7: No matter (driver will set it to "1"s)


The chip has some kind of basic protection against transmission errors.
When reading the state, there is a four complement bits.
The driver is checking this complement, and when it is wrong then it is
returning I/O error.

When writing output, the master must repeat the PIO Output Data byte in
its inverted form and it is waiting for a confirmation.
If the write is unsuccessful for three times, the write also returns
I/O error.