projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 7f15b664 M |
1 | Kernel driver pcf8574 |
| 2 | ===================== | |
| 3 | ||
| 4 | Supported chips: | |
| 5 | * Philips PCF8574 | |
| 6 | Prefix: 'pcf8574' | |
| 7 | Addresses scanned: I2C 0x20 - 0x27 | |
| 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: I2C 0x38 - 0x3f | |
| 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@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 | ||
| 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 | ! Be careful ! | |
| 42 | The PCF8574(A) is plainly impossible to detect ! Stupid chip. | |
| 43 | So every chip with address in the interval [20..27] and [38..3f] are | |
| 44 | detected as PCF8574(A). If you have other chips in this address | |
| 45 | range, the workaround is to load this module after the one | |
| 46 | for your others chips. | |
| 47 | ||
| 48 | On detection (i.e. insmod, modprobe et al.), directories are being | |
| 49 | created for each detected PCF8574(A): | |
| 50 | ||
| 51 | /sys/bus/i2c/devices/<0>-<1>/ | |
| 52 | where <0> is the bus the chip was detected on (e. g. i2c-0) | |
| 53 | and <1> the chip address ([20..27] or [38..3f]): | |
| 54 | ||
| 55 | (example: /sys/bus/i2c/devices/1-0020/) | |
| 56 | ||
| 57 | Inside these directories, there are two files each: | |
| 58 | read and write (and one file with chip name). | |
| 59 | ||
| 60 | The read file is read-only. Reading gives you the current I/O input | |
| 61 | if the corresponding output is set as 1, otherwise the current output | |
| 62 | value, that is to say 0. | |
| 63 | ||
| 64 | The write file is read/write. Writing a value outputs it on the I/O | |
| 553515e5 JD |
65 | port. Reading returns the last written value. As it is not possible |
| 66 | to read this value from the chip, you need to write at least once to | |
| 67 | this file before you can read back from it. |