How to recover from NACK on I2C transaction on STM32WB55

[Thibaut M.]

My STM32WB55 is configured as I2C master and connected to an I2C slave.

My I2C block is configured like this:

I2C->CR1 = 0x01

I2C->CR2 = 0x000A0060 (slave address=0x60 and NBYTES=0x0A)

To start the I2C transaction I2C->CR2.START is set to 1.

I2C communication starts, but at some point the slave send a NACK, this is expected.

 

Then, my I2C block is stuck, I acknowledge the I2C_ICR_NACKCF flag, then send another START command. I2C block send START command on the bus but never rise the `I2C->ISR.TXIS` flag, it will never send anymore byte on the bus.

An unexpected STOP is send right after the START.

Here I can see a START command is sent on the bus and acked by the slave:

How to recover from a NACK?

Datasheet shows a diagram, if a NACK is received, state is `End` but what does it mean?

stm32wb55rg_reference_manual.pdf, section 32.4.9 I2C master mode

My only workaround for now is to reset the I2C block. I attached the capture made with a Saleae device.

Despite this NACK problem, it works well.

[Remy ISSALYS · Accepted solution]

Hello,

According to the reference manual RM0434, when a NACK is received, a STOP condition is automatically sent after the NACK reception, see the following extract:

If a NACK is received: the TXIS flag is not set, and a STOP condition is automatically sent after the NACK reception. the NACKF flag is set in the I2C_ISR register, and an interrupt is generated if the NACKIE bit is set.

After the STOP, normally you don't need to restart I2C, just send another frame.

Best Regards

[B_D_R]

Hi @Remy ISSALYS,

Actually I have the issue, after sending slave address frame NACKF, STOPF,  TXE in ISR register is set.

so which another frame to be send? Slave Address Frame OR the Data which to be transmit?

Regards.