This version (19 Apr 2023 02:45) was approved by Marc Sosa, Jose Ramon San Buenaventura.The Previously approved version (18 Apr 2023 11:22) is available.Diff

MAX31865 - No-OS Driver

Supported Devices

Evaluation Boards


The MAX31865 is an easy-to-use resistance-to-digital converter optimized for platinum resistance temperature detectors (RTDs). An external resistor sets the sensitivity for the RTD being used and a precision delta-sigma ADC converts the ratio of the RTD resistance to the reference resistance into digital form.

The MAX31865’s inputs are protected against overvoltage faults as large as Q45V. Programmable detection of RTD and cable open and short conditions is included.


  • Industrial Equipment
  • Medical Equipment
  • Instrumentation


The goal of ADI Microcontroller No-OS is to provide reference projects for lower end processors, which can't run Linux or aren't running a specific operating system, and to help those customers using microcontrollers with ADI parts. ADI No-OS offers generic drivers, which can be used as a base for any microcontroller platform and also example projects, which are using these drivers on various microcontroller platforms.

For more information about ADI No-OS and supported microcontroller platforms, visit the No-OS User Guide.

MAX31865 ADI No-OS driver

Driver Source Code

The source code for MAX31865 driver can be found here:

This driver also uses the ADI utility library, so make sure you also add the necessary files to your project. The source code for the util library can be found here:

To use the MAX32865 No-OS Driver, you need to provide the specific implementation for the communication APIs and the specific types they use. If the SPI communication is chosen, there are three functions which are called by the MAX31865 driver and have to be implemented:

no_os_spi_init() initializes the communication peripheral.
no_os_spi_write_and_read() writes and reads data to/from the device.
no_os_spi_remove() deinitializes the communication peripheral.

And there are two data types that have to be defined:

no_os_spi_desc structure holding the SPI descriptor
no_os_spi_init_param structure holding the parameters for SPI initialization

An example of a header file containing the prototypes of the functions which have to be implemented, along with some generic data types they are using, can be found below:

Code Documentation

Source code documentation for the driver is automatically generated using the Doxygen tool and can be accessed in these links:

Device Configuration

Driver Initialization

To use the device, you need to provide the support for the communication protocol (SPI) as mentioned above.

The first API function to be called is max31865_init. Make sure that it returns 0. This indicates a successful driver initialization.

Bias Configuration

When no conversions are being performed, VBIAS may be disabled to reduce power dissipation. When automatic (continuous) conversion mode is selected, VBIAS remains on continuously.

max31865_enable_bias Enable or disables the bias voltage on the RTD sensor

Conversion Mode Configuration

Conversion mode is configurable between automatic conversion mode where continuous conversion is used and “Normally Off” mode where 1-shot conversion is used, this also has a selectable 50/60Hz conversion rates.

max31865_auto_convert Option for continuous conversions between 50/60 Hz
max31865_enable_50Hz Option for 50Hz or 60Hz noise filters

Fault Threshold Configuration

The High Fault Threshold and Low Fault Threshold registers select the trip thresholds for RTD fault detection. The results of RTD conversions are compared with the values in these registers to generate the “Fault” bits in the Fault Status register. The RTD Data Registers, High Fault Threshold Registers, and Low Fault Threshold Registers all have the same format.

max31865_set_threshold Update the contents of the HIGH and LOW FAULT registers of max31865
max31865_get_lower_threshold Read the raw 16-bit lower threshold value
max31865_get_upper_threshold Read the raw 16-bit upper threshold value
The RTD High bit in the Fault Status Register is set if the RTD resistance register value is greater than or equal to the value in the High Fault Threshold register. The POR value of the High Fault Threshold register is FFFFh.
The RTD Low bit in the Fault Status Register is set if the RTD resistance value is less than or equal to the value in the Low Fault Threshold register. The POR value of the Low Fault Threshold register is 0000h.

Wire Configuration

MAX31865 can be configured to support 2-wire, 3-wire and 4-wire types of RTD sensors.

max31865_set_wires N-wire option for RTD measurement setup

Driver Initialization Example

Example Initialization Using Maxim SDK as Platform

int ret;

uint16_t low_thres, high_thres, rtd_raw;

struct max_spi_init_param max31865_extra = {
	.num_slaves = 1,
	.polarity = SPI_SS_POL_LOW,

struct max31865_init_param max31865_ip = {
	.spi_init.device_id = 1,
	.spi_init.max_speed_hz = 2000000,
	.spi_init.chip_select = 0,
	.spi_init.mode = NO_OS_SPI_MODE_3,
	.spi_init.bit_order = NO_OS_SPI_BIT_ORDER_MSB_FIRST,
	.spi_init.platform_ops = &max_spi_ops,
	.spi_init.extra = &max31865_extra,

struct max31865_dev *max31865_device;

ret = max31865_init(&max31865_device, &max31865_ip);
if (ret)
	return ret;

/* Set upper and lower threshold values */
ret = max31865_set_threshold(max31865_device, 0x2121, 0x4114);
if (ret)
	return ret;

/* Obtain lower threshold value */
ret = max31865_get_lower_threshold(max31865_device, &low_thres);
if (ret)
	return ret;

/* Obtain upper threshold value*/
ret = max31865_get_upper_threshold(max31865_device, &high_thres);
	return ret;

/* Enable 50Hz filter */
ret = max31865_enable_50Hz(max31865_device, true);
if (ret)
	return ret;

/* Configure for even wire setting */
ret = max31865_set_wires(max31865_device, false);
if (ret)
	return ret;


	/* Read rtd register raw value (16 bits) */
	ret = max31865_read_rtd(max31865_device, &rtd_raw);
	if (ret)
		return ret;


}// end while


return 0;

resources/tools-software/uc-drivers/max31865.txt · Last modified: 19 Apr 2023 02:45 by Marc Sosa