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1 | Kernel driver pcf8591 | ||
2 | ===================== | ||
3 | |||
4 | Supported 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 | |||
11 | Authors: | ||
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 | |||
17 | Description | ||
18 | ----------- | ||
19 | The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one | ||
20 | analog output) for the I2C bus produced by Philips Semiconductors. It | ||
21 | is designed to provide a byte I2C interface to up to 4 separate devices. | ||
22 | |||
23 | The PCF8591 has 4 analog inputs programmable as single-ended or | ||
24 | differential 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 | |||
43 | See the datasheet for details. | ||
44 | |||
45 | Module 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 | |||
57 | Accessing PCF8591 via /sys interface | ||
58 | ------------------------------------- | ||
59 | |||
60 | ! Be careful ! | ||
61 | The PCF8591 is plainly impossible to detect ! Stupid chip. | ||
62 | So every chip with address in the interval [48..4f] is | ||
63 | detected as PCF8591. If you have other chips in this address | ||
64 | range, the workaround is to load this module after the one | ||
65 | for your others chips. | ||
66 | |||
67 | On detection (i.e. insmod, modprobe et al.), directories are being | ||
68 | created for each detected PCF8591: | ||
69 | |||
70 | /sys/bus/devices/<0>-<1>/ | ||
71 | where <0> is the bus the chip was detected on (e. g. i2c-0) | ||
72 | and <1> the chip address ([48..4f]) | ||
73 | |||
74 | Inside these directories, there are such files: | ||
75 | in0, in1, in2, in3, out0_enable, out0_output, name | ||
76 | |||
77 | Name contains chip name. | ||
78 | |||
79 | The in0, in1, in2 and in3 files are RO. Reading gives the value of the | ||
80 | corresponding channel. Depending on the current analog inputs configuration, | ||
81 | files in2 and/or in3 do not exist. Values range are from 0 to 255 for single | ||
82 | ended inputs and -128 to +127 for differential inputs (8-bit ADC). | ||
83 | |||
84 | The 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 | |||
87 | The out0_output file is RW. Writing a number between 0 and 255 (8-bit DAC), send | ||
88 | the value to the digital-to-analog converter. Note that a voltage will | ||
89 | only appears on AOUT pin if aout0_enable equals 1. Reading returns the last | ||
90 | value written. | ||