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1 | Kernel driver pcf8591 |
2 | ===================== | |
3 | ||
4 | Supported chips: | |
afc31875 | 5 | * Philips/NXP PCF8591 |
7f15b664 | 6 | Prefix: 'pcf8591' |
6dfee853 | 7 | Addresses scanned: none |
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8 | Datasheet: Publicly available at the NXP website |
9 | http://www.nxp.com/pip/PCF8591_6.html | |
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10 | |
11 | Authors: | |
12 | Aurelien Jarno <aurelien@aurel32.net> | |
13 | valuable contributions by Jan M. Sendler <sendler@sendler.de>, | |
7c81c60f | 14 | Jean Delvare <jdelvare@suse.de> |
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15 | |
16 | ||
17 | Description | |
18 | ----------- | |
afc31875 | 19 | |
7f15b664 | 20 | The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one |
afc31875 JD |
21 | analog output) for the I2C bus produced by Philips Semiconductors (now NXP). |
22 | It is designed to provide a byte I2C interface to up to 4 separate devices. | |
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23 | |
24 | The PCF8591 has 4 analog inputs programmable as single-ended or | |
25 | differential inputs : | |
26 | - mode 0 : four single ended inputs | |
27 | Pins AIN0 to AIN3 are single ended inputs for channels 0 to 3 | |
28 | ||
29 | - mode 1 : three differential inputs | |
30 | Pins AIN3 is the common negative differential input | |
31 | Pins AIN0 to AIN2 are positive differential inputs for channels 0 to 2 | |
32 | ||
33 | - mode 2 : single ended and differential mixed | |
34 | Pins AIN0 and AIN1 are single ended inputs for channels 0 and 1 | |
35 | Pins AIN2 is the positive differential input for channel 3 | |
36 | Pins AIN3 is the negative differential input for channel 3 | |
37 | ||
38 | - mode 3 : two differential inputs | |
39 | Pins AIN0 is the positive differential input for channel 0 | |
40 | Pins AIN1 is the negative differential input for channel 0 | |
41 | Pins AIN2 is the positive differential input for channel 1 | |
42 | Pins AIN3 is the negative differential input for channel 1 | |
43 | ||
44 | See the datasheet for details. | |
45 | ||
46 | Module parameters | |
47 | ----------------- | |
48 | ||
49 | * input_mode int | |
50 | ||
51 | Analog input mode: | |
52 | 0 = four single ended inputs | |
53 | 1 = three differential inputs | |
54 | 2 = single ended and differential mixed | |
55 | 3 = two differential inputs | |
56 | ||
57 | ||
58 | Accessing PCF8591 via /sys interface | |
59 | ------------------------------------- | |
60 | ||
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61 | The PCF8591 is plainly impossible to detect! Thus the driver won't even |
62 | try. You have to explicitly instantiate the device at the relevant | |
63 | address (in the interval [0x48..0x4f]) either through platform data, or | |
64 | using the sysfs interface. See Documentation/i2c/instantiating-devices | |
65 | for details. | |
7f15b664 | 66 | |
6dfee853 | 67 | Directories are being created for each instantiated PCF8591: |
7f15b664 | 68 | |
afc31875 | 69 | /sys/bus/i2c/devices/<0>-<1>/ |
6dfee853 | 70 | where <0> is the bus the chip is connected to (e. g. i2c-0) |
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71 | and <1> the chip address ([48..4f]) |
72 | ||
73 | Inside these directories, there are such files: | |
afc31875 | 74 | in0_input, in1_input, in2_input, in3_input, out0_enable, out0_output, name |
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75 | |
76 | Name contains chip name. | |
77 | ||
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78 | The in0_input, in1_input, in2_input and in3_input files are RO. Reading gives |
79 | the value of the corresponding channel. Depending on the current analog inputs | |
80 | configuration, files in2_input and in3_input may not exist. Values range | |
81 | from 0 to 255 for single ended inputs and -128 to +127 for differential inputs | |
82 | (8-bit ADC). | |
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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. |