xref: /linux/Documentation/hwmon/pcf8591.rst (revision d19e470b6605c900db21fc7b34c66b6891a79983)
1Kernel driver pcf8591
2=====================
3
4Supported chips:
5
6  * Philips/NXP PCF8591
7
8    Prefix: 'pcf8591'
9
10    Addresses scanned: none
11
12    Datasheet: Publicly available at the NXP website
13
14	       http://www.nxp.com/pip/PCF8591_6.html
15
16Authors:
17      - Aurelien Jarno <aurelien@aurel32.net>
18      - valuable contributions by Jan M. Sendler <sendler@sendler.de>,
19      - Jean Delvare <jdelvare@suse.de>
20
21
22Description
23-----------
24
25The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one
26analog output) for the I2C bus produced by Philips Semiconductors (now NXP).
27It is designed to provide a byte I2C interface to up to 4 separate devices.
28
29The PCF8591 has 4 analog inputs programmable as single-ended or
30differential inputs:
31
32- mode 0 : four single ended inputs
33	Pins AIN0 to AIN3 are single ended inputs for channels 0 to 3
34
35- mode 1 : three differential inputs
36	Pins AIN3 is the common negative differential input
37	Pins AIN0 to AIN2 are positive differential inputs for channels 0 to 2
38
39- mode 2 : single ended and differential mixed
40	Pins AIN0 and AIN1 are single ended inputs for channels 0 and 1
41	Pins AIN2 is the positive differential input for channel 3
42	Pins AIN3 is the negative differential input for channel 3
43
44- mode 3 : two differential inputs
45	Pins AIN0 is the positive differential input for channel 0
46	Pins AIN1 is the negative differential input for channel 0
47	Pins AIN2 is the positive differential input for channel 1
48	Pins AIN3 is the negative differential input for channel 1
49
50See the datasheet for details.
51
52Module parameters
53-----------------
54
55* input_mode int
56
57    Analog input mode:
58
59	 - 0 = four single ended inputs
60	 - 1 = three differential inputs
61	 - 2 = single ended and differential mixed
62	 - 3 = two differential inputs
63
64
65Accessing PCF8591 via /sys interface
66-------------------------------------
67
68The PCF8591 is plainly impossible to detect! Thus the driver won't even
69try. You have to explicitly instantiate the device at the relevant
70address (in the interval [0x48..0x4f]) either through platform data, or
71using the sysfs interface. See Documentation/i2c/instantiating-devices.rst
72for details.
73
74Directories are being created for each instantiated PCF8591:
75
76/sys/bus/i2c/devices/<0>-<1>/
77   where <0> is the bus the chip is connected to (e. g. i2c-0)
78   and <1> the chip address ([48..4f])
79
80Inside these directories, there are such files:
81
82   in0_input, in1_input, in2_input, in3_input, out0_enable, out0_output, name
83
84Name contains chip name.
85
86The in0_input, in1_input, in2_input and in3_input files are RO. Reading gives
87the value of the corresponding channel. Depending on the current analog inputs
88configuration, files in2_input and in3_input may not exist. Values range
89from 0 to 255 for single ended inputs and -128 to +127 for differential inputs
90(8-bit ADC).
91
92The out0_enable file is RW. Reading gives "1" for analog output enabled and
93"0" for analog output disabled. Writing accepts "0" and "1" accordingly.
94
95The out0_output file is RW. Writing a number between 0 and 255 (8-bit DAC), send
96the value to the digital-to-analog converter. Note that a voltage will
97only appears on AOUT pin if aout0_enable equals 1. Reading returns the last
98value written.
99