Documentation/iio/ad7944.rst

   1 .. SPDX-License-Identifier: GPL-2.0-only
   2
   3 =============
   4 AD7944 driver
   5 =============
   6
   7 ADC driver for Analog Devices Inc. AD7944 and similar devices. The module name
   8 is ``ad7944``.
   9
  10
  11 Supported devices
  12 =================
  13
  14 The following chips are supported by this driver:
  15
  16 * `AD7944 <https://www.analog.com/AD7944>`_
  17 * `AD7985 <https://www.analog.com/AD7985>`_
  18 * `AD7986 <https://www.analog.com/AD7986>`_
  19
  20
  21 Supported features
  22 ==================
  23
  24 SPI wiring modes
  25 ----------------
  26
  27 The driver currently supports three of the many possible SPI wiring configurations.
  28
  29 CS mode, 3-wire, without busy indicator
  30 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  31
  32 .. code-block::
  33
  34                                          +-------------+
  35                     +--------------------| CS          |
  36                     v                    |             |
  37     VIO   +--------------------+         |     HOST    |
  38      |    |        CNV         |         |             |
  39      +--->| SDI   AD7944   SDO |-------->| SDI         |
  40           |        SCK         |         |             |
  41           +--------------------+         |             |
  42                     ^                    |             |
  43                     +--------------------| SCLK        |
  44                                          +-------------+
  45
  46 To select this mode in the device tree, set the ``adi,spi-mode`` property to
  47 ``"single"`` and omit the ``cnv-gpios`` property.
  48
  49 CS mode, 4-wire, without busy indicator
  50 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  51
  52 .. code-block::
  53
  54                                          +-------------+
  55      +-----------------------------------| CS          |
  56      |                                   |             |
  57      |              +--------------------| GPIO        |
  58      |              v                    |             |
  59      |    +--------------------+         |     HOST    |
  60      |    |        CNV         |         |             |
  61      +--->| SDI   AD7944   SDO |-------->| SDI         |
  62           |        SCK         |         |             |
  63           +--------------------+         |             |
  64                     ^                    |             |
  65                     +--------------------| SCLK        |
  66                                          +-------------+
  67
  68 To select this mode in the device tree, omit the ``adi,spi-mode`` property and
  69 provide the ``cnv-gpios`` property.
  70
  71 Chain mode, without busy indicator
  72 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  73
  74 .. code-block::
  75
  76                                                                  +-------------+
  77                   +-------------------------+--------------------| CS          |
  78                   v                         v                    |             |
  79         +--------------------+    +--------------------+         |     HOST    |
  80         |        CNV         |    |        CNV         |         |             |
  81    +--->| SDI   AD7944   SDO |--->| SDI   AD7944   SDO |-------->| SDI         |
  82    |    |        SCK         |    |        SCK         |         |             |
  83   GND   +--------------------+    +--------------------+         |             |
  84                   ^                         ^                    |             |
  85                   +-------------------------+--------------------| SCLK        |
  86                                                                  +-------------+
  87
  88 To select this mode in the device tree, set the ``adi,spi-mode`` property to
  89 ``"chain"``, add the ``spi-cs-high`` flag, add the ``#daisy-chained-devices``
  90 property, and omit the ``cnv-gpios`` property.
  91
  92 Reference voltage
  93 -----------------
  94
  95 All 3 possible reference voltage sources are supported:
  96
  97 - Internal reference
  98 - External 1.2V reference and internal buffer
  99 - External reference
 100
 101 The source is determined by the device tree. If ``ref-supply`` is present, then
 102 the external reference is used. If ``refin-supply`` is present, then the internal
 103 buffer is used. If neither is present, then the internal reference is used.
 104
 105 Unimplemented features
 106 ----------------------
 107
 108 - ``BUSY`` indication
 109 - ``TURBO`` mode
 110
 111
 112 Device attributes
 113 =================
 114
 115 There are two types of ADCs in this family, pseudo-differential and fully
 116 differential. The channel name is different depending on the type of ADC.
 117
 118 Pseudo-differential ADCs
 119 ------------------------
 120
 121 AD7944 and AD7985 are pseudo-differential ADCs and have the following attributes:
 122
 123 +---------------------------------------+--------------------------------------------------------------+
 124 | Attribute                             | Description                                                  |
 125 +=======================================+==============================================================+
 126 | ``in_voltage0_raw``                   | Raw ADC voltage value (*IN+* referenced to ground sense).    |
 127 +---------------------------------------+--------------------------------------------------------------+
 128 | ``in_voltage0_scale``                 | Scale factor to convert raw value to mV.                     |
 129 +---------------------------------------+--------------------------------------------------------------+
 130
 131 In "chain" mode, additional chips will appear as additional voltage input
 132 channels, e.g. ``in_voltage1_raw``.
 133
 134 Fully-differential ADCs
 135 -----------------------
 136
 137 AD7986 is a fully-differential ADC and has the following attributes:
 138
 139 +---------------------------------------+--------------------------------------------------------------+
 140 | Attribute                             | Description                                                  |
 141 +=======================================+==============================================================+
 142 | ``in_voltage0-voltage1_raw``          | Raw ADC voltage value (*IN+* - *IN-*).                       |
 143 +---------------------------------------+--------------------------------------------------------------+
 144 | ``in_voltage0-voltage1_scale``        | Scale factor to convert raw value to mV.                     |
 145 +---------------------------------------+--------------------------------------------------------------+
 146
 147 In "chain" mode, additional chips will appear as additional voltage input
 148 channels, e.g. ``in_voltage2-voltage3_raw``.
 149
 150
 151 Device buffers
 152 ==============
 153
 154 This driver supports IIO triggered buffers.
 155
 156 See :doc:`iio_devbuf` for more information.