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diff --git a/Documentation/iio/ad7944.rst b/Documentation/iio/ad7944.rst new file mode 100644 index 0000000000..0d26e56aba --- /dev/null +++ b/Documentation/iio/ad7944.rst @@ -0,0 +1,156 @@ +.. 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. |