Inter-integrated circuit (I
2
C) interface RM0016
290/449 Doc ID 14587 Rev 8
Bus error (BERR)
This error occurs when the I2C interface detects an external stop or a start condition during
an address or data transfer. In this case:
● The BERR bit is set and an interrupt is generated if the ITERREN bit is set
● In the case of the slave: data are discarded and the lines are released by hardware:
– In the case of a misplaced start, the slave considers it is a restart and waits for an
address or a stop condition.
– In the case of a misplaced stop, the slave reacts in the same way as for a stop
condition and the lines are released by hardware.
● In the case of the master: the lines are not released and there is no effect in the state of
the current transmission: software can decide if it wants to abort the current
transmission or not.
Acknowledge failure (AF)
This error occurs when the interface detects a non-acknowledge bit. In this case,
● The AF bit is set and an interrupt is generated if the ITERREN bit is set
● A transmitter which receives a NACK must reset the communication:
– If slave: Lines are released by hardware
– If master: A stop condition or repeated start must be generated by software
Arbitration lost (ARLO)
This error occurs when the I2C interface detects an arbitration lost condition. In this case,
● The ARLO bit is set by hardware (and an interrupt is generated if the ITERREN bit is
set).
● The I2C interface goes automatically back to slave mode (the MSL bit is cleared)
● When the I²C loses the arbitration, it is not able to acknowledge its slave address in the
same transfer, but it can acknowledge it after a repeated start from the master.
● Lines are released by hardware
Overrun/underrun error (OVR)
An Overrun error can occur in slave mode when clock stretching is disabled and the I2C
interface is receiving data. The interface has received a byte (RXNE = 1) and the data in DR
has not been read, before the next byte is received by the interface. In this case,
● The last received byte is lost
● In case of overrun error, software should clear the RXNE bit and the transmitter should
re-transmit the last received byte.
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