AD719X no-OS driver

See drivers/adc/ad719x (doxygen) for the Doxygen documentation.

Supported Devices

• AD7190

• AD7192

• AD7193

• AD7194

• AD7195

Overview

The AD719X family are low noise, complete analog front ends for high precision measurement applications. Each device contains a low noise, 24-bit sigma-delta ADC preceded by a low noise gain stage, so that signals of small amplitude can be interfaced directly to the ADC. The on-chip channel sequencer allows several analog input channels to be enabled, and the device automatically sequences through the enabled channels.

The output data rate from the part is software-programmable and can be varied from 4.7 Hz to 4.8 kHz. A flexible digital filter is provided, offering both a fast settling option and a zero-latency option. The devices can be configured for buffered or unbuffered, bipolar or unipolar analog inputs and offer a programmable gain stage supporting gains of 1, 8, 16, 32, 64, and 128.

The AD719X can operate with an internal 4.92 MHz clock or with an external clock or crystal. On-chip features include a bridge power-down switch, an internal temperature sensor, and programmable general-purpose digital outputs. The parts communicate through a serial interface (SPI) compatible with standard microcontroller and DSP interface protocols.

Applications

• Weigh scales

• Strain gauge transducers

• Pressure measurement

• Temperature measurement

• Chromatography

• Industrial process control

• Portable instrumentation

AD719X Device Configuration

Driver Initialization

In order to be able to use the device, you will have to provide the support for the communication protocol (SPI) as well as a GPIO used to monitor the MISO/RDY line. An optional SYNC GPIO can be provided when synchronizing multiple devices.

The first API to be called is ad719x_init. Make sure that it returns 0, which means that the driver was initialized correctly. The chip_id field in the init parameters selects the target part (AD7190, AD7192, AD7193, AD7194 or AD7195). During initialization, the driver initializes the SPI and GPIOs, performs a software reset, verifies the device ID against chip_id, and then applies the initial range/gain, output data rate, buffer, clock source and operating mode from the init parameters. The input mode is applied only on the AD7193 and AD7194, and the bridge power-down switch is configured on every part except the AD7194.

Note that ad719x_init takes the init parameters structure by value, while spi_init, gpio_miso and sync_pin are supplied as pointers inside it. The sync_pin is optional (it may be NULL) and is only needed when synchronizing multiple devices.

Register Access

Low-level register access is available through ad719x_set_register_value, ad719x_get_register_value and ad719x_set_masked_register_value, which read and write the 8-, 24- or 32-bit device registers (Communications, Status, Mode, Configuration, Data, ID, GPOCON, Offset and Full-Scale). Use ad719x_reset to return the device to its default state.

Operating Modes and Synchronization

Use ad719x_set_operating_mode to place the device into one of its operating modes: continuous conversion, single conversion, idle, power-down, or one of the zero-scale/full-scale internal and system calibration modes (see enum ad719x_adc_modes). ad719x_wait_rdy_go_low polls the MISO/RDY line and blocks until a conversion result is ready (or an internal timeout expires).

Channel and Input Configuration

ad719x_channels_select enables one or more analog input channels using a channel mask (see the AD719X_CH_* defines and AD719X_CH_MASK). The number of selectable channels depends on the part, so the accepted mask width differs (up to 10 bits on the AD7193, 9 bits on the AD7194, 8 bits on the others); an out-of-range mask returns -EINVAL.

ad719x_config_input_mode selects between differential and pseudo-differential inputs; it is only supported on the AD7193 and AD7194 and returns -ENOTSUP on the other parts. ad719x_buffer_select enables or disables the input buffer. ad719x_range_setup selects the conversion polarity (0 = bipolar, 1 = unipolar) together with the ADC input range (gain of 1, 8, 16, 32, 64 or 128, see enum ad719x_adc_gain).

Filter and Clock Configuration

ad719x_output_rate_select sets the filter update (output data) rate code (1 to 1023). ad719x_clock_select selects the clock source: external crystal, external clock on MCLK2, or the internal 4.92 MHz clock (see enum ad719x_adc_clock).

Calibration

ad719x_calibrate performs the requested calibration (internal/system, zero-scale/full-scale) on the specified channel.

Measurement and Conversion

ad719x_single_conversion returns the result of a single conversion, while ad719x_continuous_read_avg averages a configurable number of samples. ad719x_temperature_read reads the internal temperature sensor and returns the value in degrees Celsius. ad719x_convert_to_millivolts converts a 24-bit raw conversion result to millivolts for a given reference voltage, accounting for the currently configured polarity and gain.

Bridge Power-Down Switch

ad719x_set_bridge_switch opens (0) or closes (1) the bridge power-down switch (GPOCON BPDSW), which can be used to disconnect a bridge sensor between conversions to save power. It is not available on the AD7194 and returns -ENOTSUP on that part.

AD719X Driver Initialization Example

struct ad719x_dev *dev;
int ret;
uint32_t raw_data;
float millivolts;

struct no_os_spi_init_param spi_init = {
        .device_id = SPI_DEVICE_ID,
        .max_speed_hz = SPI_MAX_SPEED,
        .chip_select = SPI_CS,
        .mode = NO_OS_SPI_MODE_3,
        .bit_order = NO_OS_SPI_BIT_ORDER_MSB_FIRST,
        .platform_ops = SPI_OPS,
        .extra = SPI_EXTRA,
};

struct no_os_gpio_init_param gpio_miso = {
        .number = GPIO_MISO_NUMBER,
        .port = GPIO_MISO_PORT,
        .platform_ops = GPIO_OPS,
        .extra = GPIO_EXTRA,
};

struct ad719x_init_param init_param = {
        .spi_init = &spi_init,
        .gpio_miso = &gpio_miso,
        .sync_pin = NULL,
        .chip_id = AD7193,
        .current_polarity = 0,
        .current_gain = AD719X_ADC_GAIN_1,
        .operating_mode = AD719X_MODE_SINGLE,
        .data_rate_code = 480,
        .clock_source = AD719X_INT_CLK_4_92_MHZ,
        .input_mode = 0,
        .buffer = 1,
        .bpdsw_mode = 0,
};

ret = ad719x_init(&dev, init_param);
if (ret)
        goto error;

/* Configure range and read a single conversion on channel 0 */
ret = ad719x_range_setup(dev, 0, AD719X_ADC_GAIN_1);
if (ret)
        goto error_remove;

ret = ad719x_channels_select(dev, AD719X_CH_MASK(AD719X_CH_0));
if (ret)
        goto error_remove;

ret = ad719x_single_conversion(dev, &raw_data);
if (ret)
        goto error_remove;

millivolts = ad719x_convert_to_millivolts(dev, raw_data, 2.5);

error_remove:
        ad719x_remove(dev);
error:
        return ret;