要檢測信號上升沿的話，可以采用以下方法：
always@(posedge clk or negedge rst)
if(!rst)
begin sign_1b <= 1'b0; sign_2b <= 1'b0; end
else
begin sign_1b <= sign; sign_2b <= sign_1b; end
always@(posedge clk or negedge rst)
if(!rst)
sign_pos <= 1'b0;
else if (sign_2b && !sign_1b)
sign_pos <= 1'b1;
else
sign_pos <= 1'b0;