新手请教啦~

assign neg_rs232_rx = rs232_rx3 & rs232_rx2 & ~rs232_rx1 & ~rs232_rx0;这句话是什么意思啊=_=

capture this signal negedge of input signal ,such as 'rs232_rx0' if you have following code....
input rs232_rx;
reg rs232_rx3,rs232_rx2,rs232_rx1,rs232_rx0,
assign rs232_rx0 = rs232_rx;
assign neg_rs232_rx = rs232_rx3 & rs232_rx2 & ~rs232_rx1 & ~rs232_rx0;
always @(sys_clk)
begin
   rs232_rx3 <= rs232_rx2;
   rs232_rx2 <= rs232_rx1;
   rs232_rx1 <= rs232_rx0;
end

一般用于滤波\去抖,
如rs232_rx空闲为1,则neg_rs232_rx =0( ~rs232_rx0 =0,~rs232_rx1 =0,rs232_rx2 =1,rs232_rx3 =1);当rs232_rx为0,产生下降沿,则在第一个CLK,rs232_rx0 =0,此时neg_rs232_rx 仍然为0;下一个CLK,rs232_rx0 =0,rs232_rx1 =0,此时neg_rs232_rx =1;再下一个CLK,neg_rs232_rx =0
可以看出,neg_rs232_rx 产生了一个CLK的高电平.可以用来确认事件的开始.