Figure 2-3 Case 2 - SYSREF in Zone 11

In this case SYSREF is advanced such that the SYSREF comes well before the reference clock rising edge, falling into zone 11. The SYSREF Alignment Detector would display 0x3FF. Now even if we advance the SYSREF further we keep seeing SYSREF Alignment Detector output to be 0x3FF until SYSREF doesn't come before the falling edge of previous reference clock (Fref).