A robust state machine is provided for controlling a slave interface to an
I.sup.2 C-bus. The state machine is configured to enforce the
slave-device-protocol of the I.sup.2 C specification, and to provide
recovery from anomalous master-device behavior. In accordance with this
invention, the state transitions of the state machine at the slave-device
are controlled by the master-device's control of the SCL line of the
I.sup.2 C-bus, except if a START condition is detected. The state machine
is configured to asynchronously respond to a START condition on the
I.sup.2 C-bus, regardless of its current state, to force the state machine
to a known state. In the known state following the START condition, the
slave-device terminates any transmissions to the I.sup.2 C-bus, thereby
minimizing subsequent interference on the bus.
