How to handle IIC bus while the slave hold the SDA low

[jjyeh1976]

Posted on October 12, 2009 at 15:29

How to handle IIC bus while the slave hold the SDA low

[jjyeh1976]

Posted on May 17, 2011 at 15:05

Hi,

I'm using the STM8S105K4 with a IIC slave device, while power-on, the IIC bus always in the 'busy' state, that is , the SDA line always low. How can

I overcome this issue? (NOT use HW Reset.., thanks)

Jason

[mozra27]

Posted on May 17, 2011 at 15:05

Hi Jason,

The External pull-up resistances (4.7k) are needed on SCL and SDA, please check this point.

Regards

mozra

[jjyeh1976]

Posted on May 17, 2011 at 15:05

Hi,

Both the SDA & SCL are pulled high with 4.7K resistor.

I can access the I2C slave in debug, while first time

power on, the slave seems hold the SDA low (I don't know

why), if I press ''reset'' button, the mcu and the I2C

slave work well.

I'vd see a document of Silabs's C8051 series, they handled

such problem by changing the SDA & SCL pin to GPO mode (open

drain) and wait for SDA high, but I don't know how to

configure the STM8S105 from alternate function (I2C) to

GPO mode, any idea?

regards,

Jason

[mozra27]

Posted on May 17, 2011 at 15:05

Hi Jason,

It can happen that it is the master that forces the line in the low state!!! What is the master device used in your case?

The SDA & SCl are configured as alternate function when enabling the I2C, you don't have access to reconfigure the I/O as alternate function but you can add a software pull-up on the I/O:

GPIOE->CR1 = 0x06;

Please try this and keep us informed

Regards

mozra