| 1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465 |
- Kernel driver pcf8574
- =====================
- Supported chips:
- * Philips PCF8574
- Prefix: 'pcf8574'
- Addresses scanned: none
- Datasheet: Publicly available at the Philips Semiconductors website
- http://www.semiconductors.philips.com/pip/PCF8574P.html
- * Philips PCF8574A
- Prefix: 'pcf8574a'
- Addresses scanned: none
- Datasheet: Publicly available at the Philips Semiconductors website
- http://www.semiconductors.philips.com/pip/PCF8574P.html
- Authors:
- Frodo Looijaard <frodol@dds.nl>,
- Philip Edelbrock <phil@netroedge.com>,
- Dan Eaton <dan.eaton@rocketlogix.com>,
- Aurelien Jarno <aurelien@aurel32.net>,
- Jean Delvare <khali@linux-fr.org>,
- Description
- -----------
- The PCF8574(A) is an 8-bit I/O expander for the I2C bus produced by Philips
- Semiconductors. It is designed to provide a byte I2C interface to up to 16
- separate devices (8 x PCF8574 and 8 x PCF8574A).
- This device consists of a quasi-bidirectional port. Each of the eight I/Os
- can be independently used as an input or output. To setup an I/O as an
- input, you have to write a 1 to the corresponding output.
- For more informations see the datasheet.
- Accessing PCF8574(A) via /sys interface
- -------------------------------------
- The PCF8574(A) is plainly impossible to detect ! Stupid chip.
- So, you have to pass the I2C bus and address of the installed PCF857A
- and PCF8574A devices explicitly to the driver at load time via the
- force=... parameter.
- On detection (i.e. insmod, modprobe et al.), directories are being
- created for each detected PCF8574(A):
- /sys/bus/i2c/devices/<0>-<1>/
- where <0> is the bus the chip was detected on (e. g. i2c-0)
- and <1> the chip address ([20..27] or [38..3f]):
- (example: /sys/bus/i2c/devices/1-0020/)
- Inside these directories, there are two files each:
- read and write (and one file with chip name).
- The read file is read-only. Reading gives you the current I/O input
- if the corresponding output is set as 1, otherwise the current output
- value, that is to say 0.
- The write file is read/write. Writing a value outputs it on the I/O
- port. Reading returns the last written value. As it is not possible
- to read this value from the chip, you need to write at least once to
- this file before you can read back from it.
|
