|author||Bart Van Assche <firstname.lastname@example.org>||2008-01-27 18:14:45 +0100|
|committer||Jean Delvare <email@example.com>||2008-01-27 18:14:45 +0100|
|parent||i2c-ibm_iic: Whitespace cleanup (diff)|
i2c: Add support for the PCF8575 chip
Signed-off-by: Bart Van Assche <firstname.lastname@example.org> Signed-off-by: Jean Delvare <email@example.com>
Diffstat (limited to 'Documentation')
1 files changed, 72 insertions, 0 deletions
diff --git a/Documentation/i2c/chips/pcf8575 b/Documentation/i2c/chips/pcf8575
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+About the PCF8575 chip and the pcf8575 kernel driver
+The PCF8575 chip is produced by the following manufacturers:
+ * Philips NXP
+ * Texas Instruments
+Some vendors sell small PCB's with the PCF8575 mounted on it. You can connect
+such a board to a Linux host via e.g. an USB to I2C interface. Examples of
+PCB boards with a PCF8575:
+ * SFE Breakout Board for PCF8575 I2C Expander by RobotShop
+ * Breakout Board for PCF8575 I2C Expander by Spark Fun Electronics
+The PCF8575 chip is a 16-bit I/O expander for the I2C bus. Up to eight of
+these chips can be connected to the same I2C bus. You can find this
+chip on some custom designed hardware, but you won't find it on PC
+The PCF8575 chip consists of a 16-bit quasi-bidirectional port and an I2C-bus
+interface. Each of the sixteen I/O's can be independently used as an input or
+an output. To set up an I/O pin as an input, you have to write a 1 to the
+For more information please see the datasheet.
+There is no method known to detect whether a chip on a given I2C address is
+a PCF8575 or whether it is any other I2C device. So there are two alternatives
+to let the driver find the installed PCF8575 devices:
+- Load this driver after any other I2C driver for I2C devices with addresses
+ in the range 0x20 .. 0x27.
+- Pass the I2C bus and address of the installed PCF8575 devices explicitly to
+ the driver at load time via the probe=... or force=... parameters.
+For each address on which a PCF8575 chip was found or forced the following
+files will be created under /sys:
+where bus is the I2C bus number (0, 1, ...) and address is the four-digit
+hexadecimal representation of the 7-bit I2C address of the PCF8575
+(0020 .. 0027).
+The read file is read-only. Reading it will trigger an I2C read and will hence
+report the current input state for the pins configured as inputs, and the
+current output value for the pins configured as outputs.
+The write file is read-write. Writing a value to it will configure all pins
+as output for which the corresponding bit is zero. Reading the write file will
+return the value last written, or -EAGAIN if no value has yet been written to
+the write file.
+On module initialization the configuration of the chip is not changed -- the
+chip is left in the state it was already configured in through either power-up
+or through previous I2C write actions.