pcf8591.rst 3.1 KB

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