学习摘自数字芯片实验室
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B、施密特触发
C、方波
增强抗干扰能力,避免误触发。
列出所有情况A[3:0] = 4’b0000 ~ 4’b1111即可
rst_n为异步复位,然后在每个clk上升沿进行触发器状态更新
建立时间:
Clk_delay_ff2 + T > Clk_delay_ff1 + Tco + Tcomb + Tsetup
0.8ns + 4ns > 1ns + 1.2ns + 2.2ns +0.6ns
4.8ns > 5ns,所以建立时间不满足
保持时间:
Clk_delay_ff1 + Tco+ Tcomb > Clk_delay_ff2+ Thold
1ns + 1.2ns + 2.2ns > 0.8ns + 0.3ns
4.4ns > 1.1ns,所以保持时间满足
所谓分频器就是计数器的输出状态,奇数分频器需要同时用到上升沿和下降沿。
根据输入寄存器控制分频计数值
divider.v
module divider(
input clk ,
input rst_n ,
input [2:0] divider_num ,
output reg out_clk
);
reg [2:0] divider_num_reg ;
always@(posedge clk or negedge rst_n) begin
if(!rst_n) begin
divider_num_reg <= 0 ;
end
else begin
divider_num_reg <= divider_num ;
end
end
reg [2:0] count ;
always@(posedge clk or negedge rst_n) begin
if(!rst_n) begin
count <= 0 ;
out_clk <= 0 ;
end
else begin
count <= count +1 ;
if(count == (divider_num_reg-1))begin
out_clk <= ~out_clk ;
count <= 0 ;
end
end
end
always@(negedge clk or negedge rst_n) begin
if(!rst_n) begin
count <= 0 ;
out_clk <= 0 ;
end
else begin
count <= count +1 ;
if(count == (divider_num_reg-1))begin
out_clk <= ~out_clk ;
count <= 0 ;
end
end
end
endmodule
divider_tb.v
module divider_tb;
reg clk ;
reg rst_n ;
reg [2:0] divider_num ;
wireout_clk;
initialbegin
rst_n= 1 ;
#10 rst_n= 0 ;
#10 rst_n= 1 ;
end
initialbegin
clk= 0 ;
forever#5 clk = ~clk ;
end
initialbegin
divider_num =1 ;
#300 divider_num=2 ;
#300 divider_num=3;
#300 divider_num=4 ;
#300 divider_num=5 ;
#300 divider_num=6 ;
#300 divider_num=7 ;
#300 divider_num=8 ;
end
divider divider(
.clk(clk) ,
.rst_n(rst_n) ,
.divider_num(divider_num) ,
.out_clk(out_clk)
);
endmodule
shift[2:0] = 3’b000 :output[7:0] = inp(0)_0_0_0_0_0_0_0
shift[2:0] = 3’b001 :output[7:0] = inp(1)_ inp(0)_0_0_0_0_0_0
shift[2:0] = 3’b010 :output[7:0] = inp(2)_ inp(1)_ inp(0)_0_0_0_0_0
shift[2:0] = 3’b011 :output[7:0] = inp(3)_ inp(2)_ inp(1)_ inp(0)_0_0_0_0
shift[2:0] = 3’b100 :output[7:0] = inp(4)_inp(3)_ inp(2)_ inp(1)_inp(0)_0_0_0
shift[2:0] = 3’b101 :output[7:0] = inp(5)_inp(4)_inp(3)_ inp(2)_inp(1)_ inp(0)_0_0
shift[2:0] = 3’b110 :output[7:0] = inp(6)_inp(5)_inp(4)_inp(3)_inp(2)_ inp(1)_ inp(0)_0
shift[2:0] = 3’b111 :output[7:0] = inp(7)_inp(6)_inp(5)_inp(4)_inp(3)_inp(2)_ inp(1)_ inp(0)
上述电路为纯组合逻辑,电路功能直接由真值表可以看出。
关于Verilog实现有很多种描述方式:
1、 根据得出的电路功能行为用行为级Verilog描述:
shift_mux.v
module shift_mux(
input [7:0] inp ,
input [2:0] shift,
output reg [7:0] outp
);
always@(*) begin
case(shift)
3'b000: assign outp ={inp[0],7'b000_0000} ;
3'b001: assign outp ={inp[1],inp[0],6'b00_0000} ;
3'b010: assign outp ={inp[2],inp[1],inp[0],5'b0_0000} ;
3'b011: assign outp ={inp[3],inp[2],inp[1],inp[0],4'b0000} ;
3'b100: assign outp ={inp[4],inp[3],inp[2],inp[1],inp[0],3'b000} ;
3'b101: assign outp ={inp[5],inp[4],inp[3],inp[2],inp[1],inp[0],2'b00} ;
3'b110: assign outp ={inp[6],inp[5],inp[4],inp[3],inp[2],inp[1],inp[0],1'b0} ;
3'b111: assign outp ={inp[7],inp[6],inp[5],inp[4],inp[3],inp[2],inp[1],inp[0]} ;
endcase
end
endmodule
shift_mux_tb.v
module shift_mux_tb;
reg [7:0] inp;
reg [2:0] shift;
wire [7:0] outp;
initialbegin
inp = 0 ;
shift = 0 ;
end
always#10 inp = $random%256 ;
always#10 shift = $random%8 ;
shift_muxshift_mux(
.inp(inp) ,
.shift(shift),
.outp(outp)
);
endmodule
interface_change.v
module interface_change(
input clka ,
input wra_n,
input da ,
inputclkb ,
output [7:0] db ,
outputwrb
);
reg [7:0] data = 0 ;
always@(posedge clka) begin
if(!wra_n)begin
data<= {data[6:0],da} ;
end
end
reg wra_n_reg1 ,wra_n_reg2 ;
always@(posedge clkb ) begin
wra_n_reg1<= wra_n ;
wra_n_reg2<= wra_n_reg1 ;
end
wire wra_n_check ;
assign wra_n_check = wra_n_reg1&&(!wra_n_reg2) ;
assign wrb = wra_n_check ;
assign db = (wra_n_check == 1'b1) ? data :0 ;
endmodule
interface_change_tb .v
module interface_change_tb ;
reg clka ;
reg wra_n;
reg da ;
regclkb ;
wire[7:0] db ;
wirewrb ;
initial begin
clka = 0 ;
#3;
clkb = 0 ;
end
initial begin
wra_n= 1 ;
@(posedgeclka) wra_n = 0 ;
da= $random%2 ;
@(posedgeclka) wra_n = 0 ;
da= $random%2 ;
@(posedgeclka) wra_n = 0 ;
da= $random%2 ;
@(posedgeclka) wra_n = 0 ;
da= $random%2 ;
@(posedgeclka) wra_n = 0 ;
da= $random%2 ;
@(posedgeclka) wra_n = 0 ;
da= $random%2 ;
@(posedgeclka) wra_n = 0 ;
da= $random%2 ;
@(posedgeclka) wra_n = 0 ;
da= $random%2 ;
@(posedgeclka) wra_n = 1;
end
always #5 clka = ~clka ;
always #10 clkb = ~clkb ;
interface_change interface_change (
.clka(clka) ,
.wra_n(wra_n),
.da(da) ,
.clkb(clkb),
.db(db),
.wrb(wrb)
);
endmodule