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STM32F407VG ( F4 discovery board) I2C issue

Question asked by anton.bogdan on May 12, 2014
Latest reply on May 19, 2014 by gusonela.septian
Hi guys,  i have a problem regarding comunicating with a sensor via i2c.
This is my first atempt to use i2c comunication on a ARM piece

My code for the sake of time saving is this one bellow( original from

Beside this code, i tryied other libraries with the same effect.

My sensor is hooked on PB8 for SCL, and PB9 for SDA.

I connected a logic analyzer to see whats going on, and the lines are silent...

Tryied to do some improvisations, i for example i did a loop of only these two:

while(1) {
I2Cx->CR1 |= I2C_CR1_START;
I2Cx->CR1 |= I2C_CR1_STOP;

And from above i can see on the i2c lines that i have a start and a stop signal, wich it indicates for me that the GPIO is configure right.

Using this code bellow, and like i said before tryied other i2c libs, the result is i cant send any data, for the moment i tryied only to see that the sending data is ok, but its not... there is nothing happeling on the bus lines.
As IDE i use IAR ewarm 6.30.
Any ideas whats wrong? I got no errors on the compilator, or debugger

#include <stm32f4xx.h>
#include <stm32f4xx_i2c.h>
#include <stm32f4xx_i2c.c>
#include "stm32f4xx_gpio.c"
#include "stm32f4xx_rcc.c"
#define SLAVE_ADDRESS 0x3D // the slave address (example)
void init_I2C1(void){
GPIO_InitTypeDef GPIO_InitStruct;
I2C_InitTypeDef I2C_InitStruct;
// enable APB1 peripheral clock for I2C1
RCC_APB1PeriphClockCmd(RCC_APB1Periph_I2C1, ENABLE);
// enable clock for SCL and SDA pins
/* setup SCL and SDA pins
* You can connect I2C1 to two different
* pairs of pins:
* 1. SCL on PB6 and SDA on PB7
* 2. SCL on PB8 and SDA on PB9
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9; // we are going to use PB6 and PB7
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;   // set pins to alternate function
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;  // set GPIO speed
GPIO_InitStruct.GPIO_OType = GPIO_OType_OD; // set output to open drain --> the line has to be only pulled low, not driven high
GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;   // enable pull up resistors
GPIO_Init(GPIOB, &GPIO_InitStruct); // init GPIOB
// Connect I2C1 pins to AF
GPIO_PinAFConfig(GPIOB, GPIO_PinSource8, GPIO_AF_I2C1); // SCL
GPIO_PinAFConfig(GPIOB, GPIO_PinSource9, GPIO_AF_I2C1); // SDA
// configure I2C1
I2C_InitStruct.I2C_ClockSpeed = 100000; // 100kHz
I2C_InitStruct.I2C_Mode = I2C_Mode_I2C; // I2C mode
I2C_InitStruct.I2C_DutyCycle = I2C_DutyCycle_2; // 50% duty cycle --> standard
I2C_InitStruct.I2C_OwnAddress1 = 0x00;  // own address, not relevant in master mode
I2C_InitStruct.I2C_Ack = I2C_Ack_Disable;   // disable acknowledge when reading (can be changed later on)
I2C_InitStruct.I2C_AcknowledgedAddress = I2C_AcknowledgedAddress_7bit; // set address length to 7 bit addresses
I2C_Init(I2C1, &I2C_InitStruct);    // init I2C1
// enable I2C1
I2C_Cmd(I2C1, ENABLE);
/* This function issues a start condition and
* transmits the slave address + R/W bit
* Parameters:
* I2Cx --> the I2C peripheral e.g. I2C1
* address --> the 7 bit slave address
* direction --> the tranmission direction can be:
* I2C_Direction_Tranmitter for Master transmitter mode
* I2C_Direction_Receiver for Master receiver
void I2C_start(I2C_TypeDef* I2Cx, uint8_t address, uint8_t direction){
// wait until I2C1 is not busy anymore
while(I2C_GetFlagStatus(I2Cx, I2C_FLAG_BUSY));
// Send I2C1 START condition
I2C_GenerateSTART(I2Cx, ENABLE);
// wait for I2C1 EV5 --> Slave has acknowledged start condition
while(!I2C_CheckEvent(I2Cx, I2C_EVENT_MASTER_MODE_SELECT));
// Send slave Address for write
I2C_Send7bitAddress(I2Cx, address, direction);
/* wait for I2C1 EV6, check if
* either Slave has acknowledged Master transmitter or
* Master receiver mode, depending on the transmission
* direction
if(direction == I2C_Direction_Transmitter){
else if(direction == I2C_Direction_Receiver){
/* This function transmits one byte to the slave device
* Parameters:
* I2Cx --> the I2C peripheral e.g. I2C1
* data --> the data byte to be transmitted
void I2C_write(I2C_TypeDef* I2Cx, uint8_t data)
I2C_SendData(I2Cx, data);
// wait for I2C1 EV8_2 --> byte has been transmitted
/* This function reads one byte from the slave device
* and acknowledges the byte (requests another byte)
uint8_t I2C_read_ack(I2C_TypeDef* I2Cx){
// enable acknowledge of recieved data
I2C_AcknowledgeConfig(I2Cx, ENABLE);
// wait until one byte has been received
while( !I2C_CheckEvent(I2Cx, I2C_EVENT_MASTER_BYTE_RECEIVED) );
// read data from I2C data register and return data byte
uint8_t data = I2C_ReceiveData(I2Cx);
return data;
/* This function reads one byte from the slave device
* and doesn't acknowledge the recieved data
uint8_t I2C_read_nack(I2C_TypeDef* I2Cx){
// disabe acknowledge of received data
// nack also generates stop condition after last byte received
// see reference manual for more info
I2C_AcknowledgeConfig(I2Cx, DISABLE);
I2C_GenerateSTOP(I2Cx, ENABLE);
// wait until one byte has been received
while( !I2C_CheckEvent(I2Cx, I2C_EVENT_MASTER_BYTE_RECEIVED) );
// read data from I2C data register and return data byte
uint8_t data = I2C_ReceiveData(I2Cx);
return data;
/* This funtion issues a stop condition and therefore
* releases the bus
void I2C_stop(I2C_TypeDef* I2Cx){
// Send I2C1 STOP Condition
I2C_GenerateSTOP(I2Cx, ENABLE);
int main(void){
init_I2C1(); // initialize I2C peripheral
uint8_t received_data[2];
I2C_start(I2C1, SLAVE_ADDRESS<<1, I2C_Direction_Transmitter); // start a transmission in Master transmitter mode
I2C_write(I2C1, 0x20); // write one byte to the slave
I2C_write(I2C1, 0x03); // write another byte to the slave
I2C_stop(I2C1); // stop the transmission
I2C_start(I2C1, SLAVE_ADDRESS<<1, I2C_Direction_Receiver); // start a transmission in Master receiver mode
received_data[0] = I2C_read_ack(I2C1); // read one byte and request another byte
received_data[1] = I2C_read_nack(I2C1); // read one byte and don't request another byte, stop transmission