fb4504fe84
Directory drivers/i2c/chips is going away, so drivers there must find new homes. For the pcf8591 driver, the best choice seems to be the hwmon subsystem. While the Philips PCF8591 device isn't a typical hardware monitoring chip, its DAC interface is compatible with the hwmon one, so it fits somewhat. If a better subsystem is ever created for ADC/DAC chips, the driver could be moved there. Signed-off-by: Jean Delvare <khali@linux-fr.org> Cc: Aurelien Jarno <aurelien@aurel32.net>
91 lines
3.2 KiB
Plaintext
91 lines
3.2 KiB
Plaintext
Kernel driver pcf8591
|
|
=====================
|
|
|
|
Supported chips:
|
|
* Philips PCF8591
|
|
Prefix: 'pcf8591'
|
|
Addresses scanned: I2C 0x48 - 0x4f
|
|
Datasheet: Publicly available at the Philips Semiconductor website
|
|
http://www.semiconductors.philips.com/pip/PCF8591P.html
|
|
|
|
Authors:
|
|
Aurelien Jarno <aurelien@aurel32.net>
|
|
valuable contributions by Jan M. Sendler <sendler@sendler.de>,
|
|
Jean Delvare <khali@linux-fr.org>
|
|
|
|
|
|
Description
|
|
-----------
|
|
The PCF8591 is an 8-bit A/D and D/A converter (4 analog inputs and one
|
|
analog output) for the I2C bus produced by Philips Semiconductors. It
|
|
is designed to provide a byte I2C interface to up to 4 separate devices.
|
|
|
|
The PCF8591 has 4 analog inputs programmable as single-ended or
|
|
differential inputs :
|
|
- mode 0 : four single ended inputs
|
|
Pins AIN0 to AIN3 are single ended inputs for channels 0 to 3
|
|
|
|
- mode 1 : three differential inputs
|
|
Pins AIN3 is the common negative differential input
|
|
Pins AIN0 to AIN2 are positive differential inputs for channels 0 to 2
|
|
|
|
- mode 2 : single ended and differential mixed
|
|
Pins AIN0 and AIN1 are single ended inputs for channels 0 and 1
|
|
Pins AIN2 is the positive differential input for channel 3
|
|
Pins AIN3 is the negative differential input for channel 3
|
|
|
|
- mode 3 : two differential inputs
|
|
Pins AIN0 is the positive differential input for channel 0
|
|
Pins AIN1 is the negative differential input for channel 0
|
|
Pins AIN2 is the positive differential input for channel 1
|
|
Pins AIN3 is the negative differential input for channel 1
|
|
|
|
See the datasheet for details.
|
|
|
|
Module parameters
|
|
-----------------
|
|
|
|
* input_mode int
|
|
|
|
Analog input mode:
|
|
0 = four single ended inputs
|
|
1 = three differential inputs
|
|
2 = single ended and differential mixed
|
|
3 = two differential inputs
|
|
|
|
|
|
Accessing PCF8591 via /sys interface
|
|
-------------------------------------
|
|
|
|
! Be careful !
|
|
The PCF8591 is plainly impossible to detect ! Stupid chip.
|
|
So every chip with address in the interval [48..4f] is
|
|
detected as PCF8591. If you have other chips in this address
|
|
range, the workaround is to load this module after the one
|
|
for your others chips.
|
|
|
|
On detection (i.e. insmod, modprobe et al.), directories are being
|
|
created for each detected PCF8591:
|
|
|
|
/sys/bus/devices/<0>-<1>/
|
|
where <0> is the bus the chip was detected on (e. g. i2c-0)
|
|
and <1> the chip address ([48..4f])
|
|
|
|
Inside these directories, there are such files:
|
|
in0, in1, in2, in3, out0_enable, out0_output, name
|
|
|
|
Name contains chip name.
|
|
|
|
The in0, in1, in2 and in3 files are RO. Reading gives the value of the
|
|
corresponding channel. Depending on the current analog inputs configuration,
|
|
files in2 and/or in3 do not exist. Values range are from 0 to 255 for single
|
|
ended inputs and -128 to +127 for differential inputs (8-bit ADC).
|
|
|
|
The out0_enable file is RW. Reading gives "1" for analog output enabled and
|
|
"0" for analog output disabled. Writing accepts "0" and "1" accordingly.
|
|
|
|
The out0_output file is RW. Writing a number between 0 and 255 (8-bit DAC), send
|
|
the value to the digital-to-analog converter. Note that a voltage will
|
|
only appears on AOUT pin if aout0_enable equals 1. Reading returns the last
|
|
value written.
|