1Kernel driver pcf8591
2=====================
3
4Supported chips:
5  * Philips/NXP PCF8591
6    Prefix: 'pcf8591'
7    Addresses scanned: none
8    Datasheet: Publicly available at the NXP website
9               http://www.nxp.com/pip/PCF8591_6.html
10
11Authors:
12        Aurelien Jarno <aurelien@aurel32.net>
13        valuable contributions by Jan M. Sendler <sendler@sendler.de>,
14        Jean Delvare <jdelvare@suse.de>
15
16
17Description
18-----------
19
20The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one
21analog output) for the I2C bus produced by Philips Semiconductors (now NXP).
22It is designed to provide a byte I2C interface to up to 4 separate devices.
23
24The PCF8591 has 4 analog inputs programmable as single-ended or
25differential 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
44See the datasheet for details.
45
46Module 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
58Accessing PCF8591 via /sys interface
59-------------------------------------
60
61The PCF8591 is plainly impossible to detect! Thus the driver won't even
62try. You have to explicitly instantiate the device at the relevant
63address (in the interval [0x48..0x4f]) either through platform data, or
64using the sysfs interface. See Documentation/i2c/instantiating-devices
65for details.
66
67Directories are being created for each instantiated PCF8591:
68
69/sys/bus/i2c/devices/<0>-<1>/
70where <0> is the bus the chip is connected to (e. g. i2c-0)
71and <1> the chip address ([48..4f])
72
73Inside these directories, there are such files:
74in0_input, in1_input, in2_input, in3_input, out0_enable, out0_output, name
75
76Name contains chip name.
77
78The in0_input, in1_input, in2_input and in3_input files are RO. Reading gives
79the value of the corresponding channel. Depending on the current analog inputs
80configuration, files in2_input and in3_input may not exist. Values range
81from 0 to 255 for single ended inputs and -128 to +127 for differential inputs
82(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.
91