The sample mode defines how the 81150A / 81160A is sampling the
externally provided data stream. In fixed sampling mode there is a fix
relation between the sampling time and the rising edge of the TRIGGER-OUT
signal. In automatic sampling mode, the 81150A / 81160A is searching for
an initial transition and then samples at the configured data rate. Transition
search is being restarted after a certain time of inactivity at the input.