module jianfaqi(
RST,//复位端
CLK,//时钟输入端
Q,//计数输出端
);
input RST;
input CLK;
output reg [2:0]Q;
always @( posedge CLK or negedge RST )
begin
if (RST==0)
Q <= 3'b000;
else
Q <= Q - 1'b1;
end
endmodule
仿真的时序图: