Feedback selection is only available when Phase Alignment is selected. When phase alignment is not selected, the output feedback is directly connected to the input feedback. For designs with phase alignment, choose automatic control on-chip if you want the feedback path to match the insertion delay for CLK_OUT1 . You can also select user-controlled feedback if the feedback is in external code. If the path is completely on the FPGA, select on-chip; otherwise, select off-chip. For designs that require external feedback and related I/O logic, choose automatic control off-chip feedback. You can choose either single-ended or differential feedback in this mode. The Wizard generates the core logic and the logic required to route the feedback signals to the I/O. The Output Clocks IDE tab ( This Figure ) provides information to configure the rest of the clocking network.
Note: When you select the UltraScale PLL, choosing clocking feedback option is not available.