AD7124 no-OS Driver

Supported Devices

• AD7124-4

• AD7124-8

Overview

The AD7124-4 and AD7124-8 are low power, low noise, completely integrated analog front ends for high precision measurement applications. Both devices contain a low noise, 24-bit Σ-∆ ADC with an integrated PGA (gain 1 to 128), a reference buffer, and an on-chip temperature sensor. Up to 8 setups can be independently configured with different gains, filter types, output data rates, reference sources, and polarity modes, allowing each input channel to be optimized for its specific signal.

Communication is via a 4-wire SPI-compatible interface supporting up to 5 MHz. The ADC supports multiple operating modes including continuous, single, standby, and power-down, as well as system and internal calibration modes.

Applications

• Industrial process control

• Temperature measurement (RTD, thermocouple)

• Pressure and load cell measurement

• Weigh scales

• Medical instrumentation

• Chromatography

Operation Modes

Mode	Description
AD7124_CONTINUOUS	ADC converts continuously; DRDY pulses low after each conversion. Default operating mode.
AD7124_SINGLE	ADC performs one conversion then returns to IDLE automatically. DRDY asserts once and remains high after data is read.
AD7124_STANDBY	Low power standby; faster wake-up than power-down. Reference buffers may be kept on.
AD7124_POWER_DOWN	Lowest power state; full wake-up cycle required before the next conversion.
AD7124_IDLE	ADC stopped; registers accessible. Used before reconfiguring channels or setups.
AD7124_INT_ZERO_SCALE_CALIB	Internal zero-scale (offset) calibration.
AD7124_INT_FULL_SCALE_CALIB	Internal full-scale (gain) calibration.
AD7124_SYS_ZERO_SCALE_OFF	System zero-scale offset calibration; requires the zero-scale signal to be applied externally.
AD7124_SYS_ZERO_SCALE_GAIN	System full-scale gain calibration; requires the full-scale signal to be applied externally.

Device Configuration

Initialization and Deinitialization

ad7124_setup() allocates and initializes the device descriptor, performs a hardware reset, writes ADC control, configuration, and channel registers, and sets the power and operating mode. ad7124_remove() releases all allocated SPI and memory resources.

Register Access

Low-level register access is provided by ad7124_read_register2() and ad7124_write_register2(), which take a register enum and a 32-bit value. The legacy ad7124_read_register() / ad7124_write_register() wrappers take a struct ad7124_st_reg pointer. Direct register access is intended only for the base driver itself; upper layers should use the semantic helpers.

Channel and Setup Helpers

These functions provide a clean, register-read-based API for querying and modifying per-channel and per-setup state. All channel queries resolve the assigned setup by reading the hardware CH_MAP register, so they always reflect the current hardware configuration:

• ad7124_get_ch_setup() — returns the setup index (0-7) assigned to a hardware channel.

• ad7124_get_bipolar() / ad7124_get_pga() — read polarity and PGA bits (0-7, where gain = 2^pga_bits) for a hardware channel via its setup's Config register.

• ad7124_get_vref_mv() / ad7124_set_vref_mv() — get/set the reference voltage (mV) stored per setup in the driver descriptor. Defaults to 2500 mV (internal 2.5 V reference) for all setups at init time.

• ad7124_get_odr_ch() / ad7124_set_odr_ch() — get/set the output data rate (Hz) for a hardware channel, resolving the setup from hardware and delegating to ad7124_get_odr() / ad7124_set_odr().

Filter Configuration

Filter type is selected per setup using the ad7124_filter_type enum, which mirrors the Linux kernel AD7124 driver:

• ad7124_get_filter_type() — decodes the hardware Filter register (FILTER, REJ60, POST_FILTER fields) into an ad7124_filter_type enum.

• ad7124_set_filter_type() — encodes the enum back into the hardware Filter register.

• ad7124_get_3db_filter_factor() — returns the 3 dB cutoff factor ×1000 for a given filter type. Multiply by ODR and divide by 1000 to get the 3 dB frequency in Hz.

Filter Type	3 dB Factor ×1000
sinc4	230
sinc3	272
sinc3_pf1	633
sinc3_pf2	605
sinc3_pf3	669
sinc3_pf4	759
sinc3_sinc1 / sinc4_sinc1	272 / 230

Calibration

ad7124_do_calibration() performs a system zero-scale or full-scale calibration on the specified hardware channel. It enables the channel, sets the appropriate calibration mode, waits for completion via ad7124_wait_for_conv_ready(), then restores continuous conversion mode.

Temperature Sensor

ad7124_read_temp_raw() reads one 24-bit raw sample from the on-chip temperature sensor using hardware channel 15 and setup 7. It configures the channel (bipolar, internal reference, PGA=1, AINP=TEMP_SENSOR, AINM=AVSS), writes the Filter_7 register from the software cache to ensure a valid ODR before starting a single conversion, then disables the channel. The raw value is converted to temperature by the IIO layer using:

temperature_mC = (raw + offset) * scale
temperature_°C = temperature_mC / 1000

With the default parameters (offset = -12090248, scale = 0.073242 mC/LSB) a raw value of ~12.4 M at room temperature (~22 °C) is typical.

IIO Interface

The IIO driver (iio_ad7124.c) exposes nine channels:

• voltage0–voltage7 (IIO indices 0-7): differential voltage channels mapped to hardware channels 0, 2, 4, 6, 8, 10, 12, 14.

• temp0 (IIO index 8): on-chip temperature sensor, hardware channel 15.

All channels use a 24-bit unsigned (offset binary), big-endian scan type with 32-bit storage.

Voltage Channel Attributes

Attribute	Access	Description
raw	R	Single raw ADC conversion result.
scale	R/W	LSB value in mV. Write to change PGA.
scale_available	R	All 8 valid scale values (PGA 1-128).
offset	R	-2^23 (bipolar) or 0 (unipolar).
sampling_frequency	R/W	Output data rate in Hz.
filter_low_pass_3db_frequency	R	3 dB cutoff: factor × ODR / 1000.
filter_type	R/W	Active filter (e.g. sinc4, sinc3_pf2).
filter_type_available	R	All 10 supported filter names.
sys_calibration	W	Trigger system calibration (write-only).
sys_calibration_mode	R/W	"zero_scale" or "full_scale".
sys_calibration_mode_available	R	"zero_scale full_scale"

Temperature Channel Attributes

Attribute	Access	Description
raw	R	Single raw ADC sample from temp sensor.
scale	R	0.073242 milli-°C per LSB (fixed).
offset	R	-12090248 (fixed).
sampling_frequency	R/W	Output data rate in Hz.

Driver Initialization Example

#include "ad7124.h"
#include "iio_ad7124.h"
#include "no_os_spi.h"

extern struct ad7124_st_reg ad7124_init_regs_default[];

struct no_os_spi_init_param spi_ip = {
        .device_id    = 0,
        .max_speed_hz = 1000000,
        .chip_select  = 0,
        .mode         = NO_OS_SPI_MODE_3,
        .platform_ops = &max_spi_ops,
        .extra        = &spi_extra,
};

struct ad7124_init_param ad7124_ip = {
        .spi_init        = &spi_ip,
        .regs            = ad7124_init_regs_default,
        .spi_rdy_poll_cnt = 1000,
        .active_device   = ID_AD7124_8,
};

struct ad7124_dev *dev;
int ret;

ret = ad7124_setup(&dev, &ad7124_ip);
if (ret) {
        printf("AD7124 init failed (%d)\n", ret);
        return ret;
}

/* Optionally set external reference voltage for setup 0 */
ret = ad7124_set_vref_mv(dev, 0, 4096);
if (ret)
        goto remove;

/* Set filter type on setup 0 to sinc3 post-filter 2 */
ret = ad7124_set_filter_type(dev, 0, AD7124_FILTER_TYPE_SINC3_PF2);
if (ret)
        goto remove;

/* Read temperature */
int32_t temp_raw;
ret = ad7124_read_temp_raw(dev, &temp_raw);
if (ret)
        goto remove;

/* temperature_mC = (temp_raw - 12090248) * 0.073242 */

remove:

ad7124_remove(dev);