[PATCH] I2C: update max6875 documentation

Supported chips:

  * Maxim MAX6874, MAX6875

    Prefix: 'max6875'

    Addresses scanned: 0x50, 0x52

    Addresses scanned: None (see below)

    Datasheet:

        http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf

Author: Ben Gardner <bgardner@wabtec.com>

Module Parameters

-----------------

* allow_write int

  Set to non-zero to enable write permission:

  *0: Read only

   1: Read and write

Description

-----------

The Maxim MAX6874 is a similar, mostly compatible device, with more intputs

and outputs:

             vin     gpi    vout

MAX6874        6       4       8

MAX6875        4       3       5

MAX6874 chips can have four different addresses (as opposed to only two for

the MAX6875). The additional addresses (0x54 and 0x56) are not probed by

this driver by default, but the probe module parameter can be used if

needed.

See the datasheet for details on how to program the EEPROM.

See the datasheet for more information.

Sysfs entries

-------------

eeprom_user   - 512 bytes of user-defined EEPROM space. Only writable if

                allow_write was set and register 0x43 is 0.

eeprom_config - 70 bytes of config EEPROM. Note that changes will not get

                loaded into register space until a power cycle or device reset.

reg_config    - 70 bytes of register space. Any changes take affect immediately.

eeprom        - 512 bytes of user-defined EEPROM space.

General Remarks

---------------

A typical application will require that the EEPROMs be programmed once and

never altered afterwards.

Valid addresses for the MAX6875 are 0x50 and 0x52.

Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56.

The driver does not probe any address, so you must force the address.

Example:

$ modprobe max6875 force=0,0x50

The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple

addresses.  For example, for address 0x50, it also reserves 0x51.

The even-address instance is called 'max6875', the odd one is 'max6875-dummy'.

Programming the chip using i2c-dev

----------------------------------

Use the i2c-dev interface to access and program the chips.

Reads and write are performed differently depending on the address range.

The configuration registers are at addresses 0x00 - 0x45.

Use i2c_smbus_write_byte_data() to write a register and

i2c_smbus_read_byte_data() to read a register.

The command is the register number.

Examples:

To write a 1 to register 0x45:

  i2c_smbus_write_byte_data(fd, 0x45, 1);

To read register 0x45:

  value = i2c_smbus_read_byte_data(fd, 0x45);

The configuration EEPROM is at addresses 0x8000 - 0x8045.

The user EEPROM is at addresses 0x8100 - 0x82ff.

Use i2c_smbus_write_word_data() to write a byte to EEPROM.

The command is the upper byte of the address: 0x80, 0x81, or 0x82.

The data word is the lower part of the address or'd with data << 8.

  cmd = address >> 8;

  val = (address & 0xff) | (data << 8);

Example:

To write 0x5a to address 0x8003:

  i2c_smbus_write_word_data(fd, 0x80, 0x5a03);

Reading data from the EEPROM is a little more complicated.

Use i2c_smbus_write_byte_data() to set the read address and then

i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data.

Example:

To read data starting at offset 0x8100, first set the address:

  i2c_smbus_write_byte_data(fd, 0x81, 0x00);

And then read the data

  value = i2c_smbus_read_byte(fd);

  or

  count = i2c_smbus_read_i2c_block_data(fd, 0x84, buffer);

The block read should read 16 bytes.

0x84 is the block read command.

See the datasheet for more details.