TCA9555: TCA9555 I2C dead-lock recovery

Hello Gaston,

"I wonder if it would be possible to restart the I2C bus to the IDLE state in some way using the SDA and SCL lines. Is this feasible?"

The only method I know of is to send 18 clock pulses on SCL to try to reset the state machine though it could be possible it is in an unknown state and not respond to this.

If this does not work, then the only way to reset the device would be to do a power cycle (turn off and back on).

Thanks,

-Bobby

Hello Bobby,

Interesting... Where can I find some information about this 'resuscitation' method? Is it related to a specific functionality of the device or is it part of I2C specification?

regards,
gaston

Hello Gaston,

"Where can I find some information about this 'resuscitation' method?"

This is specified in I2C  standard though I mention 18 clock pulses to be sure the device releases the bus the standard states 9 clock pulses.

Here is a snip-it on page 20 of the standard:

"Is it related to a specific functionality of the device"

-No as this should work with all I2C slaves. It is because the slave's state machine is no longer in alignment with the actual I2C clock. This could happen because of noise, hot plug event, parasitic inductance generating ringing on the line, or cross talk to the I2C clock line. The 9 clock pulses should reset the state machine of the slave so it can see a stop condition.

I should mention as well that there are some devices out there with a feature called "stuck bus recovery" which will actually detect if the SDA line is latched low and will automatically generate 9 clock pulses to try to release the bus.

Thanks,

-Bobby