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69 lines
2.4 KiB
69 lines
2.4 KiB
Kernel driver pcf8574
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=====================
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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
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Datasheet: Publicly available at the Philips Semiconductors website
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http://www.semiconductors.philips.com/pip/PCF8574P.html
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* Philips PCF8574A
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Prefix: 'pcf8574a'
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Addresses scanned: I2C 0x38 - 0x3f
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Datasheet: Publicly available at the Philips Semiconductors website
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http://www.semiconductors.philips.com/pip/PCF8574P.html
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Authors:
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Frodo Looijaard <frodol@dds.nl>,
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Philip Edelbrock <phil@netroedge.com>,
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Dan Eaton <dan.eaton@rocketlogix.com>,
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Aurelien Jarno <aurelien@aurel32.net>,
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Jean Delvare <khali@linux-fr.org>,
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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-bidirectional 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 /sys 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 address 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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/sys/bus/i2c/devices/<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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(example: /sys/bus/i2c/devices/1-0020/)
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Inside these directories, there are two files each:
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read and write (and one file with chip name).
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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 returns the last written value.
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On module initialization the chip is configured as eight inputs (all
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outputs to 1), so you can connect any circuit to the PCF8574(A) without
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being afraid of short-circuit.
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