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authorLinus Torvalds <torvalds@linux-foundation.org>2009-09-23 09:30:48 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-23 09:30:48 -0700
commit40aba218969914d1b225e742617adb921cf94eae (patch)
tree663ec9cdadbedec5f8eab754cbc590298c1d40be /Documentation/i2c/chips/pcf8575
parentb64ada6b23d4a305fb3ca59b79dd38707fc53b69 (diff)
parentcfd550ed3d3bd509b475c7a9d425fc63bf843a7c (diff)
Merge branch 'i2c-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jdelvare/staging
* 'i2c-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jdelvare/staging: i2c: Clearly mark ACPI drivers as such i2c: Add driver for SMBus Control Method Interface i2c-pnx: Correct use of request_region/request_mem_region MAINTAINERS: Add maintainer for AT24 and PCA9564/PCA9665 i2c-piix4: Add AMD SB900 SMBus device ID i2c/chips: Remove deprecated pcf8574 driver i2c/chips: Remove deprecated pca9539 driver i2c/chips: Remove deprecated pcf8575 driver gpio/pcf857x: Copy i2c_device_id from old pcf8574 driver i2c/scx200_acb: Provide more information on bus errors i2c: Provide compatibility links for i2c adapters i2c: Convert i2c adapters to bus devices i2c: Convert i2c clients to a device type i2c/tsl2550: Use combined SMBus transactions i2c-taos-evm: Switch echo off to improve performance i2c: Drop unused i2c_driver.id field
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-About the PCF8575 chip and the pcf8575 kernel driver
-====================================================
-
-The PCF8575 chip is produced by the following manufacturers:
-
- * Philips NXP
- http://www.nxp.com/#/pip/cb=[type=product,path=50807/41735/41850,final=PCF8575_3]|pip=[pip=PCF8575_3][0]
-
- * Texas Instruments
- http://focus.ti.com/docs/prod/folders/print/pcf8575.html
-
-
-Some vendors sell small PCB's with the PCF8575 mounted on it. You can connect
-such a board to a Linux host via e.g. an USB to I2C interface. Examples of
-PCB boards with a PCF8575:
-
- * SFE Breakout Board for PCF8575 I2C Expander by RobotShop
- http://www.robotshop.ca/home/products/robot-parts/electronics/adapters-converters/sfe-pcf8575-i2c-expander-board.html
-
- * Breakout Board for PCF8575 I2C Expander by Spark Fun Electronics
- http://www.sparkfun.com/commerce/product_info.php?products_id=8130
-
-
-Description
------------
-The PCF8575 chip is a 16-bit I/O expander for the I2C bus. Up to eight of
-these chips can be connected to the same I2C bus. You can find this
-chip on some custom designed hardware, but you won't find it on PC
-motherboards.
-
-The PCF8575 chip consists of a 16-bit quasi-bidirectional port and an I2C-bus
-interface. Each of the sixteen I/O's can be independently used as an input or
-an output. To set up an I/O pin as an input, you have to write a 1 to the
-corresponding output.
-
-For more information please see the datasheet.
-
-
-Detection
----------
-
-There is no method known to detect whether a chip on a given I2C address is
-a PCF8575 or whether it is any other I2C device, so you have to pass the I2C
-bus and address of the installed PCF8575 devices explicitly to the driver at
-load time via the force=... parameter.
-
-/sys interface
---------------
-
-For each address on which a PCF8575 chip was found or forced the following
-files will be created under /sys:
-* /sys/bus/i2c/devices/<bus>-<address>/read
-* /sys/bus/i2c/devices/<bus>-<address>/write
-where bus is the I2C bus number (0, 1, ...) and address is the four-digit
-hexadecimal representation of the 7-bit I2C address of the PCF8575
-(0020 .. 0027).
-
-The read file is read-only. Reading it will trigger an I2C read and will hence
-report the current input state for the pins configured as inputs, and the
-current output value for the pins configured as outputs.
-
-The write file is read-write. Writing a value to it will configure all pins
-as output for which the corresponding bit is zero. Reading the write file will
-return the value last written, or -EAGAIN if no value has yet been written to
-the write file.
-
-On module initialization the configuration of the chip is not changed -- the
-chip is left in the state it was already configured in through either power-up
-or through previous I2C write actions.