How to Use SPI Communication in STM32 Microcontroller

In our previous tutorials, we have learned about SPI and I2C communication between two Arduino boards. In this tutorial we will replace one Arduino board with the Blue Pill board that is STM32F103C8 and will communicate with the Arduino board using SPI bus. In this STM32 SPI Example, we will use Arduino UNO as Slave and STM32F103C8 as Master with Two 16X2 LCD display attached to each other separately. Two Potentiometers are also connected with STM32 (PA0) and Arduino (A0) to determine the sending values (0 to 255) from master to slave and slave to master by varying the potentiometer.

 

 

SPI in STM32F103C8

Comparing SPI bus in Arduino & STM32F103C8 Blue Pill board, STM32 has 2 SPI bus in it while Arduino Uno has one SPI bus. Arduino Uno has ATMEGA328 microcontroller in it, and STM32F103C8 has ARM Cortex- M3 which makes it faster than Arudino Board.

 

To learn more about SPI communication, refer our previous articles

 

• How to use SPI in Arduino: Communication between two Arduino Boards
• SPI Communication with PIC Microcontroller PIC16F877A
• SPI communication via Bit Banging
• Raspberry Pi Hot Water Tank Leak Detector using SPI Modules
• ESP32 Real Time Clock using DS3231 Module

 

STM32 SPI Pins STM32F103C8

 

 

SPI Line1	Pin in STM32F103C8
MOSI1	PA7 or PB5
MISO1	PA6 or PB4
SCK1	PA5 or PB3
SS1	PA4 or PA15
SPI Line2
MOSI2	PB15
MISO2	PB14
SCK2	PB13
SS2	PB12

 

SPI Pins in Arduino

 

 

SPI Line	Pin in Arduino
MOSI	11 or ICSP-4
MISO	12 or ICSP-1
SCK	13 or ICSP-3
SS	10

Components Required

• STM32F103C8
• Arduino
• LCD 16x2 - 2
• 10k Potentiometer – 4
• Breadboard
• Connecting Wires

 

Circuit Diagram and Connections for STM32 SPI Tutorial

 

 

The Table Below shows the Pins Connected for STM32 SPI communication with Arduino.

SPI Pin	STM32F103C8	Arduino
MOSI	PA7	11
MISO	PA6	12
SCK	PA5	13
SS1	PA4	10

 

The table below shows the pins connected for Two LCD (16x2) with STM32F103C8 and Arduino separately.

LCD pin	STM32F103C8	Arduino
VSS	GND	GND
VDD	+5V	+5V
V0	To Potentiometer Centre PIN for LCD contrast	To Potentiometer Centre PIN for LCD contrast
RS	PB0	2
RW	GND	GND
E	PB1	3
D4	PB10	4
D5	PB11	5
D6	PC13	6
D7	PC14	7
A	+5V	+5V
K	GND	GND

 

Important:

• Don’t forget to connect the Arduino GND and STM32F103C8 GND together.

 

STM32 SPI Programming

The programming is similar to the Arduino code. The same <SPI.h> library is used in programming STM32F103C8. It can be programmed using USB port without using FTDI programmer, to learn more about programming STM32 with Arduino IDE follow the link.

 

In this STM32 SPI Example, we will use Arduino UNO as Slave and STM32F103C8 as Master with Two 16X2 LCD display attached to each other separately. Two Potentiometers are also connected with STM32 (PA0) and Arduino (A0) to determine the sending values (0 to 255) from master to slave and slave to master by varying the potentiometer.

Analog input is taken at STM32F10C8 pin PA0 (0 to 3.3V) by rotating the potentiometer. Then this input value is converted into Analog to Digital value (0 to 4096) and this digital value is further mapped to (0 to 255) as we can send only 8-bit (byte) data through SPI communication at once.

Similarly in Slave side we take analog input value at Arduino pin A0 from (0 to 5V) by using potentiometer. And again this input value is converted into Analog to Digital value (0 to 1023) and this digital value is further mapped to (0 to 255)

 

This tutorial has two programs one for master STM32 and other for slave Arduino. Complete programs for both the sides are given at the end of this project with a demonstration Video.

 

Master STM32 SPI Programming Explanation

1. First of all we need to include the SPI library for using SPI communication functions and LCD library for using LCD functions. Also define LCD pins for 16x2 LCD. Learn more about interfacing LCD with STM32 here.

#include<SPI.h>    
#include<LiquidCrystal.h> 
const int rs = PB0, en = PB1, d4 = PB10 , d5 = PB11 , d6 = PC13, d7 = PC14;  
LiquidCrystal lcd(rs,en,d4,d5,d6,d7);

 

2. In void setup()

• Start Serial Communication at Baud Rate 9600.

Serial.begin(9600);  

             

• Next begin the SPI communication

SPI.begin(); 

                         

• Then set the Clock divider for SPI communication. I have set divider 16.

SPI.setClockDivider(SPI_CLOCK_DIV16);   

 

• Next set the SS pin HIGH since we didn’t start any transfer to slave arduino.

digitalWrite(SS,HIGH);                 

        

3. In void loop()

• Before sending any value to slave we need to LOW the slave select value to begin transfer to slave from master.

digitalWrite(SS, LOW);        

 

• Next read the analog value from the master STM32F10C8 POT attached to pin PA0.

int pot = analogRead(PA0);                      

 

Then convert this value in terms of one byte (0 to 255).

byte MasterSend = map(pot,0,4096,0,255);        

 

• Here comes the important step, in the following statement we send the converted POT value stored in Mastersend variable to the slave Arduino, and also receive value from slave Arduino and stored that in mastereceive variable.

 Mastereceive = SPI.transfer(Mastersend);

 

• Next display those received values from the slave arduino    with a delay of 500 microseconds and then continuously receive and display the values.

Serial.println("Slave Arduino to Master STM32");                               
Serial.println(MasterReceive  lcd.setCursor(0,0);                                                         
 lcd.print("Master: STM32");
 lcd.setCursor(0,1);                                                   
 lcd.print("SalveVal:");                                                         
 lcd.print(MasterReceive  delay(500);
 digitalWrite(SS, HIGH);  

 

Note: We use serial.println() to view the result in Serial Motor of Arduino IDE.

 

Slave Arduino SPI Programming Explanation

1. Same as master, first of all we need to include the SPI library for using I2C communication functions and LCD library for using LCD functions. Also define LCD pins for 16x2 LCD.

#include<SPI.h>  
#include<LiquidCrystal.h> 
 LiquidCrystal lcd(2, 3, 4, 5, 6, 7);    // Define LCD Module Pins (RS,EN,D4,D5,D6,D7)

 

2. In void setup()

• We Start Serial Communication at Baud Rate 9600.

Serial.begin(9600);               

 

• Below statement sets MISO as OUTPUT (Have to Send data to Master IN).So data is sent via MISO of Slave Arduino.

pinMode(MISO,OUTPUT);                  

 

• Now Turn on SPI in Slave Mode by using SPI Control Register

SPCR |= _BV(SPE);                    

 

• Then turn ON interrupt for SPI communication. If a data is received from master the Interrupt Service Routine is called and the received value is taken from SPDR (SPI data Register)

SPI.attachInterrupt();         

   

• The value from master is taken from SPDR and stored in Slavereceived variable. This takes place in following Interrupt Routine function.

ISR (SPI_STC_vect)
{
  Slavereceived = SPDR;                  
  received = true;                       
}

 

3. Next in void loop ()

• Read the analog value from the Slave Arduino POT attached to pin A0.

int pot = analogRead(A0);                     

 

• Convert that value in terms of one byte as 0 to 255. 

Slavesend = map(pot,0,1023,0,255);

 

• Next important step is to send the converted value to the Master STM32F10C8, so place the value in the SPDR register. The SPDR register is used to send and receive values.

SPDR = Slavesend;

 

• Then display the received value (SlaveReceive) from Master STM32F103C8 on LCD with a delay of 500 microseconds and then continuously receive and display those value.

 lcd.setCursor(0,0);                     
 lcd.print("Slave: Arduino");
 lcd.setCursor(0,1);                                                    
 lcd.print("MasterVal:");   
 Serial.println("Master STM32 to Slave Arduino");  
 Serial.println(SlaveReceived);                  
 lcd.print(SlaveReceived);                       
 delay(500);

 

By rotating the Potentiometer at one side, you can see the varying values on LCD on another side:

 

So this is how SPI communication takes place in STM32. Now you can interface any SPI sensor with STM32 board.

The complete coding for Master STM32 and Slave Arduino is given below with a demonstration video