Zone trigger
Rohde & Schwarz oscilloscopes have a zone trigger to define areas on the waveform diagram that MUST or MUST NOT be intersected to trigger a signal acquisition. Such zones can be used to focus signal acquisition on dedicated signal characteristics.
The process can be applied to the DQS signal to focus on the different preamble modes or signal amplitudes of READ/WRITE bursts to test the DDR interface.
The zone trigger always operates in combination with a standard trigger event such as EDGE or pulse width. In the example below, an EDGE is applied to the DQS signal and a first zone (excluded intersect) helps focus on the start of signal bursts. Overlaying the DQ signals (persistence on) reveals that both READ and WRITE have been acquired. The edges of the DQ signal are edge-aligned with the DQS signal for READ and center-aligned for WRITE bursts.