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Mark D. Studebaker
0442f73da9
From: Aurelien Jarno <aurelien@aurel32.net> Hello, I have to use the pcf8574 chip with my I2C interface, however, the pcf8574 drivers in lm-sensors is a bit basic. It supposes the pin P1 is used as an input and the others pin as outputs. Attached is a patch which corrects that, providing to files in /proc interface, one for writting, the other for reading. It also modifies a bit the driver to support the pcf8574a (it is a pcf8574 with a different address range), and add a documentation file in doc/chips. The patch also includes some cosmetic changes in the pcf8591 driver I wrote previously, that is to say it modify the chip name in some places I had forgotten to change when I made a copy/paste from another driver. git-svn-id: http://lm-sensors.org/svn/lm-sensors/trunk@1318 7894878c-1315-0410-8ee3-d5d059ff63e0
98 lines
3.3 KiB
Plaintext
98 lines
3.3 KiB
Plaintext
Kernel driver `pcf8574.o'
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========================
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Status: Status: Complete;
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Supported chips:
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* Philips PCF8574
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Prefix: `pcf8574'
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Addresses scanned: I2C 0x20 - 0x27 (inclusive)
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Datasheet: Publicly available at the Philips Semiconductor website
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http://semiconductors.philips.com/
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* Philips PCF8574A
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Prefix: `pcf8574a'
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Addresses scanned: I2C 0x38 - 0x3f (inclusive)
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Datasheet: Publicly available at the Philips Semiconductor website
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http://semiconductors.philips.com/
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Authors: Frodo Looijaard <frodol@dds.nl>, Philip Edelbrock <phil@netroedge.com>,
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and Dan Eaton <dan.eaton@rocketlogix.com>
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Module Parameters
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-----------------
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* force: short array (min = 1, max = 48)
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List of adapter,address pairs to boldly assume to be present
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* force_pcf8574: short array (min = 1, max = 48)
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List of adapter,address pairs which are unquestionably assumed to
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contain a `pcf8574' chip
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* ignore: short array (min = 1, max = 48)
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List of adapter,address pairs not to scan
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* ignore_range: short array (min = 1, max = 48)
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List of adapter,start-addr,end-addr triples not to scan
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* probe: short array (min = 1, max = 48)
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List of adapter,address pairs to scan additionally
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* probe_range: short array (min = 1, max = 48)
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List of adapter,start-addr,end-addr triples to scan additionally
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Description
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-----------
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The PCF8574(A) is an 8-bit I/O expander for the I2C bus produced by Philips
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Semiconductors. It is designed to provide a byte I2C interface to up to 16
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separate devices (8 x PCF8574 and 8 x PCF8574A).
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This device consists of a quasi-bidirectionnal port. Each of the eight I/Os
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can be independently used as an input or output. To setup an I/O as an
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input, you have to write a 1 to the corresponding output.
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For more informations see the datasheet.
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Accessing PCF8574(A) via /proc interface
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-------------------------------------
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! Be careful !
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The PCF8574(A) is plainly impossible to detect ! Stupid chip.
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So every chip with adress in the interval [20..27] and (38..3f) are
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detected as PCF8574(A). If you have other chips in this address
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range, the workaround is to load this module after the one
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for your others chips.
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On detection (i.e. insmod, modprobe et al.), directories are being
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created for each detected PCF8574(A):
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/proc/sys/dev/sensors/pcf8574-<0>-<1>/
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where <0> is the bus the chip was detected on (e. g. i2c-0)
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and <1> the chip address ([20..27] or [38..3f]):
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./pcf8574-i2c-0-27/
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Inside these directories, there are two files each:
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read and write.
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The read file is read-only. Reading gives you the current I/O input
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if the corresponding output is set as 1, otherwise the current output
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value, that is to say 0.
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The write file is read/write. Writing a value outputs it on the I/O
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port. Reading return the last written value.
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On module initialization the chip is configured as eight I/Os input (all
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outputs to 1), so you can connect any circuit to the PCF8574(A) without
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to be afraid of short-circuit.
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Chip Features
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-------------
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Chip `pcf8574'
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LABEL LABEL CLASS COMPUTE CLASS ACCESS MAGNITUDE
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read NONE NONE R 0
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write NONE NONE RW 0
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LABEL FEATURE SYMBOL SYSCTL FILE:OFFSET
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read SENSORS_PCF8591_READ read:1
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write SENSORS_PCF8591_WRITE write:1
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