forked from luck/tmp_suning_uos_patched
553515e5c5
Do not initialize the PCF8574 with an arbitrary value. Users will have to write the initial value to sysfs themselves. Signed-off-by: Jean Delvare <khali@linux-fr.org> Acked-by: Aurelien Jarno <aurelien@aurel32.net>
68 lines
2.3 KiB
Plaintext
68 lines
2.3 KiB
Plaintext
Kernel driver pcf8574
|
|
=====================
|
|
|
|
Supported chips:
|
|
* Philips PCF8574
|
|
Prefix: 'pcf8574'
|
|
Addresses scanned: I2C 0x20 - 0x27
|
|
Datasheet: Publicly available at the Philips Semiconductors website
|
|
http://www.semiconductors.philips.com/pip/PCF8574P.html
|
|
|
|
* Philips PCF8574A
|
|
Prefix: 'pcf8574a'
|
|
Addresses scanned: I2C 0x38 - 0x3f
|
|
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
|
|
-------------------------------------
|
|
|
|
! Be careful !
|
|
The PCF8574(A) is plainly impossible to detect ! Stupid chip.
|
|
So every chip with address in the interval [20..27] and [38..3f] are
|
|
detected as PCF8574(A). If you have other chips in this address
|
|
range, the workaround is to load this module after the one
|
|
for your others chips.
|
|
|
|
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.
|