In ISE - 2023.2 English

In ISE, the following period constraints are equivalent:

NET "clk" TNM_NET = sys_clk;
TIMESPEC TS_sys_clk = PERIOD "sys_clk" 10 ns HIGH 50%;
NET "clk_IBUF_BUFG" TNM_NET = sys_clk;
TIMESPEC TS_sys_clk = PERIOD "sys_clk" 10 ns HIGH 50%;