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Commit | Line | Data |
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7f15b664 RM |
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. |