2 Where Does the Sync Signal Rise Come With Respect to the Clock Rise Edge?

To have reliable Sync operation, Sync signal needs to come on the fall edge of the clock. This can help avoid setup and hold regions of the flops inside LMX1205. What if the device generating the Sync signal do not have the option to delay the edge? Here comes the windowing feature. No matter where the Sync signal comes, windowing feature can help park this sync signal internally at the fall edge of the clock. Register(R18<5:0>, SYSREFREQ_DLY register) has to be written before doing sync operation whose value is obtained from windowing feature. In some cases, Sync signal can be periodic signal, which is internal multiple of clock period. In that case, on every low to high transition of Sync Signal, Syncing can happen. To stop that, there is an SYNC_STOP(R17<4>) option. If this bit is enabled, subsequent low to high transition on Sync Signal is ignored. All naming mentioned for the registers are as per the tics-pro Field names with tics-pro version 1.7.7.6.

As discussed previously, windowing needs to be done and then Sync. To enter into each of these modes, register have to be written as shown in Table 2-1.

When user is in Sync mode and Windowing mode, sysref signal is switched off. To get output from sysref, user has to enter Request mode post Windowing and Sync. Figure 1-2 waveforms, showing sysref output in sync mode, are just for illustration purpose of the sync feature.