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92 lines
3.2 KiB
92 lines
3.2 KiB
Kernel driver pcf8591
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=====================
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Supported chips:
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* Philips/NXP PCF8591
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Prefix: 'pcf8591'
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Addresses scanned: I2C 0x48 - 0x4f
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Datasheet: Publicly available at the NXP website
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http://www.nxp.com/pip/PCF8591_6.html
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Authors:
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Aurelien Jarno <aurelien@aurel32.net>
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valuable contributions by Jan M. Sendler <sendler@sendler.de>,
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Jean Delvare <khali@linux-fr.org>
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Description
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-----------
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The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one
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analog output) for the I2C bus produced by Philips Semiconductors (now NXP).
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It is designed to provide a byte I2C interface to up to 4 separate devices.
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The PCF8591 has 4 analog inputs programmable as single-ended or
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differential inputs :
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- mode 0 : four single ended inputs
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Pins AIN0 to AIN3 are single ended inputs for channels 0 to 3
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- mode 1 : three differential inputs
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Pins AIN3 is the common negative differential input
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Pins AIN0 to AIN2 are positive differential inputs for channels 0 to 2
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- mode 2 : single ended and differential mixed
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Pins AIN0 and AIN1 are single ended inputs for channels 0 and 1
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Pins AIN2 is the positive differential input for channel 3
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Pins AIN3 is the negative differential input for channel 3
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- mode 3 : two differential inputs
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Pins AIN0 is the positive differential input for channel 0
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Pins AIN1 is the negative differential input for channel 0
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Pins AIN2 is the positive differential input for channel 1
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Pins AIN3 is the negative differential input for channel 1
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See the datasheet for details.
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Module parameters
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-----------------
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* input_mode int
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Analog input mode:
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0 = four single ended inputs
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1 = three differential inputs
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2 = single ended and differential mixed
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3 = two differential inputs
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Accessing PCF8591 via /sys interface
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-------------------------------------
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! Be careful !
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The PCF8591 is plainly impossible to detect! Stupid chip.
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So every chip with address in the interval [0x48..0x4f] is
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detected as PCF8591. 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 PCF8591:
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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 ([48..4f])
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Inside these directories, there are such files:
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in0_input, in1_input, in2_input, in3_input, out0_enable, out0_output, name
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Name contains chip name.
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The in0_input, in1_input, in2_input and in3_input files are RO. Reading gives
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the value of the corresponding channel. Depending on the current analog inputs
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configuration, files in2_input and in3_input may not exist. Values range
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from 0 to 255 for single ended inputs and -128 to +127 for differential inputs
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(8-bit ADC).
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The out0_enable file is RW. Reading gives "1" for analog output enabled and
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"0" for analog output disabled. Writing accepts "0" and "1" accordingly.
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The out0_output file is RW. Writing a number between 0 and 255 (8-bit DAC), send
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the value to the digital-to-analog converter. Note that a voltage will
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only appears on AOUT pin if aout0_enable equals 1. Reading returns the last
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value written.
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