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author | Bart Van Assche <bart.vanassche@gmail.com> | 2008-01-27 17:14:45 (GMT) |
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committer | Jean Delvare <khali@hyperion.delvare> | 2008-01-27 17:14:45 (GMT) |
commit | 5864ae03ca982fb60bedeebfd67562db37c1ee6a (patch) | |
tree | a2c0982c544be712246e797451abb7bf850492e7 /Documentation | |
parent | 217bcec4425cdc8fb90ce688eb4d5b5140713046 (diff) | |
download | linux-5864ae03ca982fb60bedeebfd67562db37c1ee6a.tar.xz |
i2c: Add support for the PCF8575 chip
Signed-off-by: Bart Van Assche <bart.vanassche@gmail.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/i2c/chips/pcf8575 | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/Documentation/i2c/chips/pcf8575 b/Documentation/i2c/chips/pcf8575 new file mode 100644 index 0000000..25f5698 --- /dev/null +++ b/Documentation/i2c/chips/pcf8575 @@ -0,0 +1,72 @@ +About the PCF8575 chip and the pcf8575 kernel driver +==================================================== + +The PCF8575 chip is produced by the following manufacturers: + + * Philips NXP + http://www.nxp.com/#/pip/cb=[type=product,path=50807/41735/41850,final=PCF8575_3]|pip=[pip=PCF8575_3][0] + + * Texas Instruments + http://focus.ti.com/docs/prod/folders/print/pcf8575.html + + +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 + http://www.robotshop.ca/home/products/robot-parts/electronics/adapters-converters/sfe-pcf8575-i2c-expander-board.html + + * Breakout Board for PCF8575 I2C Expander by Spark Fun Electronics + http://www.sparkfun.com/commerce/product_info.php?products_id=8130 + + +Description +----------- +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 +motherboards. + +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 +corresponding output. + +For more information please see the datasheet. + + +Detection +--------- + +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. + +/sys interface +-------------- + +For each address on which a PCF8575 chip was found or forced the following +files will be created under /sys: +* /sys/bus/i2c/devices/<bus>-<address>/read +* /sys/bus/i2c/devices/<bus>-<address>/write +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. |