Based on kernel version 2.6.31. Page generated on 2009-09-16 22:26 EST.
1 About the PCF8575 chip and the pcf8575 kernel driver 2 ==================================================== 3 4 The PCF8575 chip is produced by the following manufacturers: 5 6 * Philips NXP 7 http://www.nxp.com/#/pip/cb=[type=product,path=50807/41735/41850,final=PCF8575_3]|pip=[pip=PCF8575_3][0] 8 9 * Texas Instruments 10 http://focus.ti.com/docs/prod/folders/print/pcf8575.html 11 12 13 Some vendors sell small PCB's with the PCF8575 mounted on it. You can connect 14 such a board to a Linux host via e.g. an USB to I2C interface. Examples of 15 PCB boards with a PCF8575: 16 17 * SFE Breakout Board for PCF8575 I2C Expander by RobotShop 18 http://www.robotshop.ca/home/products/robot-parts/electronics/adapters-converters/sfe-pcf8575-i2c-expander-board.html 19 20 * Breakout Board for PCF8575 I2C Expander by Spark Fun Electronics 21 http://www.sparkfun.com/commerce/product_info.php?products_id=8130 22 23 24 Description 25 ----------- 26 The PCF8575 chip is a 16-bit I/O expander for the I2C bus. Up to eight of 27 these chips can be connected to the same I2C bus. You can find this 28 chip on some custom designed hardware, but you won't find it on PC 29 motherboards. 30 31 The PCF8575 chip consists of a 16-bit quasi-bidirectional port and an I2C-bus 32 interface. Each of the sixteen I/O's can be independently used as an input or 33 an output. To set up an I/O pin as an input, you have to write a 1 to the 34 corresponding output. 35 36 For more information please see the datasheet. 37 38 39 Detection 40 --------- 41 42 There is no method known to detect whether a chip on a given I2C address is 43 a PCF8575 or whether it is any other I2C device, so you have to pass the I2C 44 bus and address of the installed PCF8575 devices explicitly to the driver at 45 load time via the force=... parameter. 46 47 /sys interface 48 -------------- 49 50 For each address on which a PCF8575 chip was found or forced the following 51 files will be created under /sys: 52 * /sys/bus/i2c/devices/<bus>-<address>/read 53 * /sys/bus/i2c/devices/<bus>-<address>/write 54 where bus is the I2C bus number (0, 1, ...) and address is the four-digit 55 hexadecimal representation of the 7-bit I2C address of the PCF8575 56 (0020 .. 0027). 57 58 The read file is read-only. Reading it will trigger an I2C read and will hence 59 report the current input state for the pins configured as inputs, and the 60 current output value for the pins configured as outputs. 61 62 The write file is read-write. Writing a value to it will configure all pins 63 as output for which the corresponding bit is zero. Reading the write file will 64 return the value last written, or -EAGAIN if no value has yet been written to 65 the write file. 66 67 On module initialization the configuration of the chip is not changed -- the 68 chip is left in the state it was already configured in through either power-up 69 or through previous I2C write actions.