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linux
1Kernel driver pcf8574
2=====================
3
4Supported 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
17Authors:
18 Frodo Looijaard <frodol@dds.nl>,
19 Philip Edelbrock <phil@netroedge.com>,
20 Dan Eaton <dan.eaton@rocketlogix.com>,
21 Aurelien Jarno <aurelien@aurel32.net>,
22 Jean Delvare <khali@linux-fr.org>,
23
24
25Description
26-----------
27The PCF8574(A) is an 8-bit I/O expander for the I2C bus produced by Philips
28Semiconductors. It is designed to provide a byte I2C interface to up to 16
29separate devices (8 x PCF8574 and 8 x PCF8574A).
30
31This device consists of a quasi-bidirectional port. Each of the eight I/Os
32can be independently used as an input or output. To setup an I/O as an
33input, you have to write a 1 to the corresponding output.
34
35For more informations see the datasheet.
36
37
38Accessing PCF8574(A) via /sys interface
39-------------------------------------
40
41The PCF8574(A) is plainly impossible to detect ! Stupid chip.
42So, you have to pass the I2C bus and address of the installed PCF857A
43and PCF8574A devices explicitly to the driver at load time via the
44force=... parameter.
45
46On detection (i.e. insmod, modprobe et al.), directories are being
47created for each detected PCF8574(A):
48
49/sys/bus/i2c/devices/<0>-<1>/
50where <0> is the bus the chip was detected on (e. g. i2c-0)
51and <1> the chip address ([20..27] or [38..3f]):
52
53(example: /sys/bus/i2c/devices/1-0020/)
54
55Inside these directories, there are two files each:
56read and write (and one file with chip name).
57
58The read file is read-only. Reading gives you the current I/O input
59if the corresponding output is set as 1, otherwise the current output
60value, that is to say 0.
61
62The write file is read/write. Writing a value outputs it on the I/O
63port. Reading returns the last written value. As it is not possible
64to read this value from the chip, you need to write at least once to
65this file before you can read back from it.