Based on kernel version 2.6.31. Page generated on 2009-09-16 22:26 EST.
1 Kernel driver pcf8574 2 ===================== 3 4 Supported chips: 5 * Philips PCF8574 6 Prefix: 'pcf8574' 7 Addresses scanned: none 8 Datasheet: Publicly available at the Philips Semiconductors website 9 http://www.semiconductors.philips.com/pip/PCF8574P.html 10 11 * Philips PCF8574A 12 Prefix: 'pcf8574a' 13 Addresses scanned: none 14 Datasheet: Publicly available at the Philips Semiconductors website 15 http://www.semiconductors.philips.com/pip/PCF8574P.html 16 17 Authors: 18 Frodo Looijaard <frodol[AT]dds[DOT]nl>, 19 Philip Edelbrock <phil[AT]netroedge[DOT]com>, 20 Dan Eaton <dan.eaton[AT]rocketlogix[DOT]com>, 21 Aurelien Jarno <aurelien[AT]aurel32[DOT]net>, 22 Jean Delvare <khali[AT]linux-fr[DOT]org>, 23 24 25 Description 26 ----------- 27 The PCF8574(A) is an 8-bit I/O expander for the I2C bus produced by Philips 28 Semiconductors. It is designed to provide a byte I2C interface to up to 16 29 separate devices (8 x PCF8574 and 8 x PCF8574A). 30 31 This device consists of a quasi-bidirectional port. Each of the eight I/Os 32 can be independently used as an input or output. To setup an I/O as an 33 input, you have to write a 1 to the corresponding output. 34 35 For more informations see the datasheet. 36 37 38 Accessing PCF8574(A) via /sys interface 39 ------------------------------------- 40 41 The PCF8574(A) is plainly impossible to detect ! Stupid chip. 42 So, you have to pass the I2C bus and address of the installed PCF857A 43 and PCF8574A devices explicitly to the driver at load time via the 44 force=... parameter. 45 46 On detection (i.e. insmod, modprobe et al.), directories are being 47 created for each detected PCF8574(A): 48 49 /sys/bus/i2c/devices/<0>-<1>/ 50 where <0> is the bus the chip was detected on (e. g. i2c-0) 51 and <1> the chip address ([20..27] or [38..3f]): 52 53 (example: /sys/bus/i2c/devices/1-0020/) 54 55 Inside these directories, there are two files each: 56 read and write (and one file with chip name). 57 58 The read file is read-only. Reading gives you the current I/O input 59 if the corresponding output is set as 1, otherwise the current output 60 value, that is to say 0. 61 62 The write file is read/write. Writing a value outputs it on the I/O 63 port. Reading returns the last written value. As it is not possible 64 to read this value from the chip, you need to write at least once to 65 this file before you can read back from it.