About I2C Bus

[lorenzo meneghello]

Posted on December 21, 2016 at 16:03

Hi all,

I'm new on ST device, i'm trying to test the I2C bus but I can't understand how it works.. I do not want to use the HAL library but manage directly the register, but the I2C Interface on ST produce the state of transmission (0x08,0x10,0x28...) like other uC? or it manages all the transmission?

Thanks.

Lorenzo.

[Nesrine M_O]

Posted on December 21, 2016 at 17:13

Hi

Meneghello.Lorenzo

‌,

• Could you please precise what are you using as STM32 product?
• Otherwise I recommend you to read carefully theInter-integrated circuit (I2C) interface section in your related reference manual to have overviewabout STM32 I2C main features and functional description.

-Nesrine-

Ifmy suggestanswers your question, please mark it as correct.

[waclawek.jan]

Posted on December 21, 2016 at 17:21

Lorenzo,

no, the I2C interface does not expose discrete states of the internal state machine as is usual in I2C peripherals following the Philips 'standard' implementation. Rather, you have to infer the internal state from various individual status bits. Read thoroughly the I2C chapter in the RM of the STM32 model of your choice. Beware, there are several evolutionary incarnations of that peripheral in various STM32 models, differing in some of the details.

JW

[lorenzo meneghello]

Posted on December 22, 2016 at 11:49

Very hard work.. There's nothing online ? example code? 

Thanks.

[Nesrine M_O]

Posted on December 22, 2016 at 12:03

Hi

Meneghello.Lorenzo

‌,

If I suppose that you are using STM32F4 product, Irecommend you to start with the examples available at ST website:

• I2C examples under the

  http://www.st.com/content/st_com/en/products/embedded-software/mcus-embedded-software/stm32-embedded-software/stm32cube-embedded-software/stm32cubef4.html

  firmware package:

  STM32Cube_FW_F4_V1.0\Projects\STM32F4-Discovery\Examples\I2C, if you are a Cube useror
• I2C examples under the

  http://www.st.com/content/st_com/en/products/embedded-software/mcus-embedded-software/stm32-embedded-software/stm32-standard-peripheral-libraries/stsw-stm32html

  http://www.st.com/content/st_com/en/products/embedded-software/mcus-embedded-software/stm32-embedded-software/stm32-standard-peripheral-libraries/stsw-stm32html

  :

  STM32F4xx_DSP_StdPeriph_Lib_V1.8.0\Project\STM32F4xx_StdPeriph_Examples\I2Cif you are SPL user

-Nesrine-

[Nor Sch]

Posted on December 22, 2016 at 13:45

The I2C itself is really simple. But to get a stable Communication between Slave and Master could take some time. I use the HAL-Driver and for Init the Driver i2c.c/.h generated from Cube. On top I have a Busdriver which is handling the Data and Transmit + Receive. Simplest Solution is to work with a State Machine. For this I have following States:

typedef enum{
 eI2C_IsErrorOccured = 0,
 eI2C_IsReadyForSend = 1,
 eI2C_IsReadyForReceive = 2,
 eI2C_IsSending = 3, //!< Status while Sending (only Bonus for Debugging, not really needed)
 eI2C_IsReceiving = 4, //!< Status while Receiving (only Bonus for Debugging, not really needed)
 eI2C_SendIsDone = 5, //!< after Tx Complete Interrupt
 eI2C_ReceiveIsDone = 6, //!< after Rx Complete Interrupt
} TE_I2C_SEND_RECEIVE_STATE;
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Build your Driver around this. Keep in Mind, that Slave and Master must have a possibility to get synchron after Errors.

Good luck!

[lorenzo meneghello]

Posted on December 22, 2016 at 17:18

Thanks all for reply, I'm trying to send a single byte but when I set the START bit on CR2, the STOPF and NACK flag will comes active.. I don't have any device on the bus..

[waclawek.jan]

Posted on December 23, 2016 at 00:53

Which STM32? How did you initialize the related GPIO pins?

JW

[lorenzo meneghello]

Posted on December 23, 2016 at 10:09

I'm using the STM32F042K6 and this is the code:

// I2C Peripheral Disable

I2C1->CR1 &= ~0x01;

//Enable the i2c

RCC->APB1ENR |= (1<<21);

RCC->CFGR3 |= (1<<4); //SYSCLK 48Mhz

//Reset the Peripheral

RCC->APB1RSTR |= (1<<21);

RCC->APB1RSTR &= ~(1<<21);

//Configure and initialize the GPIOs

GPIOA->MODER |= 0x280000;

GPIOA->OSPEEDR |= 0x280000; 

GPIOA->PUPDR |= 0x140000;

//Connect GPIO pins to peripheral

GPIOA->AFR[1] |= 0x440;

//Configure and Initialize the I2C

I2C1->TIMINGR = 0xB0420F13;

//100kHz

I2C1->OAR1 = 0;

I2C1->CR2 &= ~0x01;

//Addressing mode 7 bit

I2C1->OAR2 = 0;

I2C1->CR2 |= 0x80000;

I2C1->CR1 &= ~(1<<19);

I2C1->CR1 |= (1<<17);

// I2C Peripheral Enable

I2C1->CR1 |= 0x01;

[Jaroslav BECKA]

Posted on December 23, 2016 at 15:07

I would expect that. If you don't have any device on the bus you won't get the ACK after the START bit, address and R/W bit. That's why the NACK flag is set. You have to use another device with I2C to debug the communication. Also without a logic analyzer with I2C protocol or at least oscilloscope it may be quite challenging.