Precision Analog to Digital Converters Example Code

Introduction | Devices | Precision ADC Homepage | Repo Organization | Usage | Contribute

Introduction

Precision Analog to Digital Converters from Texas Instruments are specialized mixed signal products mainly used in signal acquisition and sensor applications. Generally, these products communicate with a micro-controller or FPGA as an SPI or I2C peripheral to configure internal settings and transmit digitized analog signals.

This repository is a collection of firmware examples for controlling, configuring, reading, and interacting with these products. You will find examples of micro-controller firmware applications which configure and operate these ADCs.

Devices

Device examples include the following products:

General Purpose ADCs:

• ADS1115 16-bit, 860-SPS, 4-channel, delta-sigma ADC with PGA, oscillator, VREF, comparator and I2C
• ADS1118 16-bit, 860-SPS, 4-channel, delta-sigma ADC with PGA, oscillator, VREF, temp sensor and SPI
• ADS1256 24-Bit, 30kSPS, 8-Ch Delta-Sigma ADC With PGA for Factory Automation and Process Control
• ADS7128 Small 8-ch 12-bit analog-to-digital converter (ADC) with I2C interface, GPIOs, CRC and RMS module

Multi-Channel Sensor Measurement:

• ADS1220 24-bit, 2-kSPS, four-channel, low-power, delta-sigma ADC with PGA, VREF, SPI and two IDACs
• ADS122C04 upcoming release
• ADS122S14 upcoming release
• ADS122U04 24-bit, 2-kSPS, 4-ch, low-power, small-size delta-sigma ADC w/ PGA, VREF, 2x IDACs & UART interface
• ADS1235 24-bit, 7.2-kSPS, 3-ch differential, delta-sigma ADC with PGA and AC excitation for bridge sensors
• ADS124S08 24-bit, 4-kSPS, 12-ch delta-sigma ADC with PGA and voltage reference for sensor measurement
• ADS1258 24-bit, 125kSPS, 16-ch delta-sigma ADC with fast channel scan and automatic sequencer
• ADS1262 32-bit 38-kSPS 10-ch delta-sigma ADC with PGA and voltage reference for factory automation

Multi-Channel Simultaneous ADCs:

• ADS131A04 24-bit 128-kSPS 4-channel simultaneous-sampling delta-sigma ADC
• ADS131B04-Q1 Automotive 24-bit, 32-kSPS, four-channel, simultaneous-sampling, delta-sigma ADC
• ADS131M08 24-bit, 32-kSPS, 8-channel, simultaneous-sampling, delta-sigma ADC

Special Purpose ADCs:

• ADS1292 24-bit, 2-ch, Low-Power Analog Front END (AFE) for ECG Applications
• ADS1299 Low-Noise, mulit-Channel, 24-Bit, Analog-to-Digital Converter for EEG and

Biopotential Measurements:

• ADS1282 Ultra-high-resolution 4-kSPS 2-channel delta-sigma ADC with PGA for seismic and energy exploration

Repo Organization

This repository is organized by individual device name. In the /devices directory, our entire catalog of example code can be found. Inside each product directory will be a set of C example code files. The'device'.cand'device'.h files will be specific to the ADC and can be used 'as is' in an embedded development environment. The hal.c and hal.h files function as a Hardware Abstraction Layer (HAL) and should be edited to match your specific processor. In some device directories there may be multiple hal.c and hal.h files which may provide the HAL functions for a variety of processors. Additionally, some devices may include complete Code Composer Studio projects or example applications. These self contained projects will have additional support functions besides the device and HAL files.

Usage

'device'.c and 'device'.h include processor agnostic functions which perform basic actions to the data converter. The 'device'.c file will include functions such as:

• initalize();
• reset();
• loadConfig();
• writeRegister(address,data);
• readRegister(address);
• readADCdata(numSamples);

Function Example:

void writeSingleRegister( SPI_Handle spiHdl, uint8_t address, uint8_t data )
{
    /* Initialize arrays */
    uint8_t DataTx[COMMAND_LENGTH + 1] = { OPCODE_WREG | (address & OPCODE_RWREG_MASK), 0, data};
    uint8_t DataRx[COMMAND_LENGTH + 1] = { 0 };

    /* Check that the register address is in range */
    assert( address < NUM_REGISTERS );

    /* Build TX array and send it */
    spiSendReceiveArrays( spiHdl, DataTx, DataRx, COMMAND_LENGTH + 1 );

    /* Update register array */
    registerMap[address] = DataTx[COMMAND_LENGTH];
}

Internal Memory

An array of registerMap[] variables are generated in order to create and store a copy of the ADCs current register values. These variables are used in multiple ways in order to speed development and communication with the ADC.

Usage case #1: When reading (or writing) register values, update the internal registerMap variable to contain the present value. Because registers can hold the values of multiple fields, updating an entire register will overwrite all fields at [address] with a new value. In order to preserve the values already present in the register, use the registerMap[] object to or the the current register value with the changing field value.

// Update register value  
    registerMap[address] = DataTx[COMMAND_LENGTH];
    writeSingleRegister( address, registerMap[address] | newFieldValueMask);
    registerMap[address] = registerMap[address] | newFieldValueMask

Usage case #2: When utilizing complex SPI or I2C interfaces, some device operations require the frame size to be adjusted. This happens, for the example, when adding a STATUS or CRC byte to the transaction. Using the internal device registerMap memory can be a fast and safe way to determine which communication method should be used.

if(registerMap[deviceConfigAddress] == CRC_Enabled)
{
spiSendRecieve(Tx,Rx,3); // send 3 word SPI frame ( includes CRC)
}
else
{
spiSendRecieve(Tx,Rx,2); // send 2 word SPI frame
}

The 'device'.h file will include device specific #definec statements to enumerate and document fields in the device register map. these definitions will provide a direct correlation to registers defined in the product data sheet.

/* ADS124S08 Register 0x1 (STATUS) Definition
 *|  Bit 7   |   Bit 6   |   Bit 5   |   Bit 4   |   Bit 3   |   Bit 2   |   Bit 1   |   Bit 0   |
 *------------------------------------------------------------------------------------------------
 *|  FL_POR  |    nRDY   | FL_P_RAILP| FL_P_RAILN| FL_N_RAILP| FL_N_RAILN| FL_REF_L1 | FL_REF_L0 |
 *------------------------------------------------------------------------------------------------
 */
    /** STATUS register address */
        #define REG_ADDR_STATUS         ((uint8_t) 0x01)

    /** STATUS default (reset) value */
	#define STATUS_DEFAULT          ((uint8_t) 0x80)
	#define ADS_FL_POR_MASK			0x80
	#define ADS_NRDY_MASK			0x40
	#define ADS_FL_P_RAILP_MASK		0x20
	#define ADS_FL_P_RAILN_MASK		0x10
	#define ADS_FL_N_RAILP_MASK		0x08
	#define ADS_FL_N_RAILN_MASK		0x04
	#define ADS_FL_REF_L1_MASK		0x02
	#define ADS_FL_REF_L0_MASK		0x10

These functions should be included in an embedded project by including the 'device'.c and 'device'.h files. Once imported, these functions can be used inline in your main application to assist in the development of higher level functions or complete applications.

Contributing to the project

• Currently we are not accepting contributions but if you have feedback for us based upon the examples provided feel free to email us