SPI Communication with STM32 and ADS1118 using CubeMx

Posted on 2019-12-02 by Burak Hamdi TUFAN

Hello everyone, In this article we are going to talk about SPI communication on STM32 and Cubemx. We are going to use HAL library in this article and make and example on communication on SPI.

Now let's get started.

I will use STM32F042 and ADS1118 for communication. ADS1118 is an Analog to Digital converter. We will fetch the values of all connected potentiometer values to our STM32F042 via ADS1118.
I HIGHLY RECOMMEND TO READ ADS1118 DATASHEET FIRST.
You can reach the datasheet via here.

Below image you can see the configuration. I selected the SPI1 hardware and Full-Dublex Communcation as Master Device I did not activate the NVIC. So I will send the parameters which I want, and then ADS1118 will send them back me.

After configuration of SPI now we will configurate the ADS1118 settings. As I mentioned before I always recommend to read datasheet first. Below table has been taken from the datasheet.

Now according to above picture we will create a register struct to manage ADS1118. We will send the parameters and set some configurations like speed, which adc port to read.


typedef union
{
    struct
    {
        volatile unsigned char    RESV  			:1;   //it does not matter 0 or 1
        volatile unsigned char    NOP         :2;
        volatile unsigned char    PULLUP      :1;
        volatile unsigned char    TS_MODE     :1;
        volatile unsigned char    DR          :3;
        volatile unsigned char    MODE        :1;
        volatile unsigned char    PGA         :3;
        volatile unsigned char    MUX         :3;
        volatile unsigned char    OS          :1;   //high
    } stru;
    volatile unsigned int  word;
    volatile unsigned char byte[2];
} ADS_InitTypeDef;


//ADS1118 Configuration Registers
ADS_InitTypeDef adsConfigReg;

Later now we need to configurate our ADS1118, to do this we have send variables to microchips' built-in registers with above structure. Below code block will do it.


	//ADS Structure variable
	ADS_InitTypeDef ConfigReg;
	
	//We will use it as single-shot mode
	adsConfigReg.stru.OS				=	0x1;   //high
	// 0x4 enables AIN0 , 0x5 enables AIN1,0x6 enables AIN2 and 0x7 enables AIN3 .
	adsConfigReg.stru.MUX			=	0x4;	
	//Programmable Gain amplifier
	adsConfigReg.stru.PGA      = 0x1;		//  FSR 4.096V 
	//Continuous mode or single-shot mode
	adsConfigReg.stru.MODE			=	0x1;
	//Data Rate register
	adsConfigReg.stru.DR       = 0x4;
	//If you want to use this chip as a temperature sensor set this as 1.
	adsConfigReg.stru.TS_MODE	=	0x0;
	//Enable built-in pull-up resistors.
	adsConfigReg.stru.PULLUP		= 0x1;
	//Command mode. Set this always as 0x01.
	adsConfigReg.stru.NOP			=	0x1;
	//Reserved register. It does not matter this register is 1 or 0.
	adsConfigReg.stru.RESV			= 0x1;
	
	Assign the values into one word belong to global variable defined above.
	adsConfigReg.word=ConfigReg->word;

	HAL_Delay(100);

I want to say something about MUX register: With this register we will set the built-in multiplexer inside the ADS1118. This multiplexer allows whic adc will be sent to the master. Also we can read differance of Analog inputs. You can get the much more information from the datasheet of ADS1118.

Now we are ready to send the parameters and get the value of selected analog input.


//Below function will send the data to the chip and fetch the result data
HAL_SPI_TransmitReceive(&hspi1,(uint8_t*)(adsConfigReg.byte), (uint8_t*) aRxBuffer, 2, 100);
//Wait a little bit
HAL_Delay(100);
//and load the data into variable.
int deger = aRxBuffer[0] | aRxBuffer[1] << 8;
//you can make the conversations for your own usage.	
float voltage_brake =  deger * 0.250;

Now we are ready to use the ADS1118.

Have a good Analog to Digital Converting :D

Burak Hamdi TUFAN