.. SPDX-License-Identifier: GPL-2.0-only
=============
AD7944 driver
=============
ADC driver for Analog Devices Inc. AD7944 and similar devices. The module name
is ``ad7944``.
Supported devices
=================
The following chips are supported by this driver:
* `AD7944 <https://www.analog.com/AD7944>`_
* `AD7985 <https://www.analog.com/AD7985>`_
* `AD7986 <https://www.analog.com/AD7986>`_
Supported features
==================
SPI wiring modes
----------------
The driver currently supports three of the many possible SPI wiring configurations.
CS mode, 3-wire, without busy indicator
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. code-block::
+-------------+
+--------------------| CS |
v | |
VIO +--------------------+ | HOST |
| | CNV | | |
+--->| SDI AD7944 SDO |-------->| SDI |
| SCK | | |
+--------------------+ | |
^ | |
+--------------------| SCLK |
+-------------+
To select this mode in the device tree, set the ``adi,spi-mode`` property to
``"single"`` and omit the ``cnv-gpios`` property.
CS mode, 4-wire, without busy indicator
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. code-block::
+-------------+
+-----------------------------------| CS |
| | |
| +--------------------| GPIO |
| v | |
| +--------------------+ | HOST |
| | CNV | | |
+--->| SDI AD7944 SDO |-------->| SDI |
| SCK | | |
+--------------------+ | |
^ | |
+--------------------| SCLK |
+-------------+
To select this mode in the device tree, omit the ``adi,spi-mode`` property and
provide the ``cnv-gpios`` property.
Chain mode, without busy indicator
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. code-block::
+-------------+
+-------------------------+--------------------| CS |
v v | |
+--------------------+ +--------------------+ | HOST |
| CNV | | CNV | | |
+--->| SDI AD7944 SDO |--->| SDI AD7944 SDO |-------->| SDI |
| | SCK | | SCK | | |
GND +--------------------+ +--------------------+ | |
^ ^ | |
+-------------------------+--------------------| SCLK |
+-------------+
To select this mode in the device tree, set the ``adi,spi-mode`` property to
``"chain"``, add the ``spi-cs-high`` flag, add the ``#daisy-chained-devices``
property, and omit the ``cnv-gpios`` property.
Reference voltage
-----------------
All 3 possible reference voltage sources are supported:
- Internal reference
- External 1.2V reference and internal buffer
- External reference
The source is determined by the device tree. If ``ref-supply`` is present, then
the external reference is used. If ``refin-supply`` is present, then the internal
buffer is used. If neither is present, then the internal reference is used.
Unimplemented features
----------------------
- ``BUSY`` indication
- ``TURBO`` mode
Device attributes
=================
There are two types of ADCs in this family, pseudo-differential and fully
differential. The channel name is different depending on the type of ADC.
Pseudo-differential ADCs
------------------------
AD7944 and AD7985 are pseudo-differential ADCs and have the following attributes:
+---------------------------------------+--------------------------------------------------------------+
| Attribute | Description |
+=======================================+==============================================================+
| ``in_voltage0_raw`` | Raw ADC voltage value (*IN+* referenced to ground sense). |
+---------------------------------------+--------------------------------------------------------------+
| ``in_voltage0_scale`` | Scale factor to convert raw value to mV. |
+---------------------------------------+--------------------------------------------------------------+
In "chain" mode, additional chips will appear as additional voltage input
channels, e.g. ``in_voltage1_raw``.
Fully-differential ADCs
-----------------------
AD7986 is a fully-differential ADC and has the following attributes:
+---------------------------------------+--------------------------------------------------------------+
| Attribute | Description |
+=======================================+==============================================================+
| ``in_voltage0-voltage1_raw`` | Raw ADC voltage value (*IN+* - *IN-*). |
+---------------------------------------+--------------------------------------------------------------+
| ``in_voltage0-voltage1_scale`` | Scale factor to convert raw value to mV. |
+---------------------------------------+--------------------------------------------------------------+
In "chain" mode, additional chips will appear as additional voltage input
channels, e.g. ``in_voltage2-voltage3_raw``.
Device buffers
==============
This driver supports IIO triggered buffers.
See :doc:`iio_devbuf` for more information.
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