Build a 4-bit shift register (right shift), with asynchronous reset, synchronous load, and enable.
- areset: Resets shift register to zero.
- load: Loads shift register with data[3:0] instead of shifting.
- ena: Shift right (q[3] becomes zero, q[0] is shifted out and disappears).
- q: The contents of the shift register.
If both the load and ena inputs are asserted (1), the load input has higher priority.
注意是上升沿复位
module top_module(
input clk,
input areset, // async active-high reset to zero
input load,
input ena,
input [3:0] data,
output reg [3:0] q);
always@ (posedge clk or posedge areset)
if(areset)
q <= 4'd0;
else if(load)
q <= data;
else if(ena)
q <= q >> 1;
endmodule