prescale_counter.pcf

该源码为xilinx ise教程的附带光盘源码

//! **************************************************************************
// Written by: Map 1.1 on Tue Dec 12 16:16:30 2006
//! **************************************************************************

SCHEMATIC START;
TIMEGRP lower_counter = BEL "counter_0" BEL "counter_1";
TIMEGRP clk = BEL "counter_0" BEL "counter_30" BEL "counter_29" BEL
        "counter_28" BEL "counter_27" BEL "counter_26" BEL "counter_25" BEL
        "counter_24" BEL "counter_23" BEL "counter_22" BEL "counter_21" BEL
        "counter_20" BEL "counter_19" BEL "counter_18" BEL "counter_17" BEL
        "counter_14" BEL "counter_16" BEL "counter_15" BEL "counter_13" BEL
        "counter_12" BEL "counter_11" BEL "counter_10" BEL "counter_9" BEL
        "counter_8" BEL "counter_7" BEL "counter_6" BEL "counter_5" BEL
        "counter_4" BEL "counter_3" BEL "counter_2" BEL "counter_1" BEL
        "counter_31";
TIMEGRP upper_counter = FFS(*) EXCEPT TIMEGRP "lower_counter";
TS_clk = PERIOD TIMEGRP "clk" 5 ns HIGH 50%;
TS_upper_counter = MAXDELAY FROM TIMEGRP "upper_counter" TO TIMEGRP
        "upper_counter" TS_clk * 4;
OFFSET = OUT 10 ns AFTER COMP "clk";
SCHEMATIC END;