Currently, the XP5IO Wizard only supports source synchronous applications where data is captured by a strobe or capture clock that is forwarded with the data. The alignment between the strobe and data can either be edge-aligned or center-aligned. The XP5IO Wizard must be set correctly to ensure proper setup and calibration algorithms are used.
When you use Edge DDR, the strobe and data are aligned. In this mode, the XP5IO PHY calibration shifts the capture clock to the center of the data eye.
Figure 1. Edge DDR
Figure 2. Center DDR
In this mode, the strobe is externally centered. The strobe is received centered to the incoming data and as a result, does not need to do any additional adjustments.