Data Bytes From Slave Are 0xff

A slave addressed by a master receiver transfer acknowledges the address byte and starts to send its data correctly, but suddenly all bytes sent by the slave are 0xff. Possible reasons are:

  • The I2C slave missed an SCL cycle because the SCL high or low-level voltages do not reach its appropriate input thresholds.
  • The I2C slave accidently interpreted a spike etc. as an SCL cycle.

After having received the last byte during a master receiver transfer, the master leaves SDA high during the acknowledge clock cycle – this causes the slave to not send data anymore, regardless whether a stop condition follows or not. Here, the slave is not synchronized anymore with the master¬†and interprets a high SDA as a “not acknowledge” from the master.

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