initial beginia = 0;ib = 1;clk = 0;#10ia = 1;	#20ib = 0;#20ia = 0;
endalways #5 clk = ~clk;

或者

initial clk = 0;initial beginia = 0;#10ia = 1;	#40ia = 0;
endinitial beginib = 1;#30 ib = 0;
endalways #5 clk = ~clk;