w1: add missing DS2413 documentation

	- This file

w1_therm

	- The Maxim/Dallas Semiconductor ds18*20 temperature sensor.

w1_ds2413

	- The Maxim/Dallas Semiconductor ds2413 dual channel addressable switch.

w1_ds2423

	- The Maxim/Dallas Semiconductor ds2423 counter device.

w1_ds28e04

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.