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R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +00001Kernel driver pcf8591
2=====================
3
4Supported chips:
5 * Philips PCF8591
6 Prefix: 'pcf8591'
7 Addresses scanned: I2C 0x48 - 0x4f
8 Datasheet: Publicly available at the Philips Semiconductor website
9 http://www.semiconductors.philips.com/pip/PCF8591P.html
10
11Authors:
12 Aurelien Jarno <aurelien@aurel32.net>
13 valuable contributions by Jan M. Sendler <sendler@sendler.de>,
14 Jean Delvare <khali@linux-fr.org>
15
16
17Description
18-----------
19The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one
20analog output) for the I2C bus produced by Philips Semiconductors. It
21is designed to provide a byte I2C interface to up to 4 separate devices.
22
23The PCF8591 has 4 analog inputs programmable as single-ended or
24differential inputs :
25- mode 0 : four single ended inputs
26 Pins AIN0 to AIN3 are single ended inputs for channels 0 to 3
27
28- mode 1 : three differential inputs
29 Pins AIN3 is the common negative differential input
30 Pins AIN0 to AIN2 are positive differential inputs for channels 0 to 2
31
32- mode 2 : single ended and differential mixed
33 Pins AIN0 and AIN1 are single ended inputs for channels 0 and 1
34 Pins AIN2 is the positive differential input for channel 3
35 Pins AIN3 is the negative differential input for channel 3
36
37- mode 3 : two differential inputs
38 Pins AIN0 is the positive differential input for channel 0
39 Pins AIN1 is the negative differential input for channel 0
40 Pins AIN2 is the positive differential input for channel 1
41 Pins AIN3 is the negative differential input for channel 1
42
43See the datasheet for details.
44
45Module parameters
46-----------------
47
48* input_mode int
49
50 Analog input mode:
51 0 = four single ended inputs
52 1 = three differential inputs
53 2 = single ended and differential mixed
54 3 = two differential inputs
55
56
57Accessing PCF8591 via /sys interface
58-------------------------------------
59
60! Be careful !
61The PCF8591 is plainly impossible to detect ! Stupid chip.
62So every chip with address in the interval [48..4f] is
63detected as PCF8591. If you have other chips in this address
64range, the workaround is to load this module after the one
65for your others chips.
66
67On detection (i.e. insmod, modprobe et al.), directories are being
68created for each detected PCF8591:
69
70/sys/bus/devices/<0>-<1>/
71where <0> is the bus the chip was detected on (e. g. i2c-0)
72and <1> the chip address ([48..4f])
73
74Inside these directories, there are such files:
75in0, in1, in2, in3, out0_enable, out0_output, name
76
77Name contains chip name.
78
79The in0, in1, in2 and in3 files are RO. Reading gives the value of the
80corresponding channel. Depending on the current analog inputs configuration,
81files in2 and/or in3 do not exist. Values range are from 0 to 255 for single
82ended inputs and -128 to +127 for differential inputs (8-bit ADC).
83
84The out0_enable file is RW. Reading gives "1" for analog output enabled and
85"0" for analog output disabled. Writing accepts "0" and "1" accordingly.
86
87The out0_output file is RW. Writing a number between 0 and 255 (8-bit DAC), send
88the value to the digital-to-analog converter. Note that a voltage will
89only appears on AOUT pin if aout0_enable equals 1. Reading returns the last
90value written.