HDLBits 移位寄存器

HDLBits

Shift4

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.

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, posedge areset) begin
        if(areset) q <= 0;
        else if(load) q <= data;
        else if(ena) q <= (q >> 1);
    end
endmodule
/* way 2:
module top_module(
	input clk,
	input areset,
	input load,
	input ena,
	input [3:0] data,
	output reg [3:0] q);
	
	// Asynchronous reset: Notice the sensitivity list.
	// The shift register has four modes:
	//   reset
	//   load
	//   enable shift
	//   idle -- preserve q (i.e., DFFs)
	always @(posedge clk, posedge areset) begin
		if (areset)		// reset
			q <= 0;
		else if (load)	// load
			q <= data;
		else if (ena)	// shift is enabled
			q <= q[3:1];	// Use vector part select to express a shift.
	end
	
endmodule
*/

Rotate100 

Build a 100-bit left/right rotator, with synchronous load and left/right enable. A rotator shifts-in the shifted-out bit from the other end of the register, unlike a shifter that discards the shifted-out bit and shifts in a zero. If enabled, a rotator rotates the bits around and does not modify/discard them.

• load: Loads shift register with data[99:0] instead of rotating.<