今天的项目是在 Verilog HDL 中实现可编程数字延迟定时器。完整呈现了延迟定时器的 Verilog 代码。
所实现的数字延迟定时器是 CMOS IC LS7212，用于生成可编程延迟。延迟定时器的规格可以在这里轻松找到。基本上，延迟定时器有 4 种操作模式：一次性 (OS)、延迟操作 (DO)、延迟释放 (DR)、双延迟 (DD)。这四种模式将通过输入 mode_a 和 mode_b 选择。
wb[7:0] 输入用于根据延迟定时器规范中给定的方程对延迟进行编程。要了解更多它在每种模式下的工作原理以及输入如何控制延迟，请参阅其数据表。以下波形显示了每种模式下延迟的产生方式。
以下是可编程数字延迟定时器 LS7212 的 Verilog 代码。
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// Verilog project: Verilog code for delay timer LS7212
module delay_timer_ls7212
(
input [7:0] wb, // weighting bits
input clk, // clock input
input reset, // timer reset
input trigger, // trigger input
input mode_a, mode_b, // mode bits A and B
output reg delay_out_n // delay output, active low
);
reg[7:0] PULSE_WIDTH ;
reg [7:0] DELAY;
reg [7:0] TIMER=0;
reg trigger_sync_1=0,trigger_sync_2=0;
wire trigger_rising,trigger_falling;
reg timer_start=0,out_low=0;
wire timer_clear2,timer_clear3,timer_clear;
reg [1:0] mode;
reg reset_timer1=0,reset_timer2=0,reset_timer=0;
wire reset_timer3,reset_det;
reg reset_det1=0,reset_det2=0;
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always @(posedge clk)
begin
trigger_sync_1 <= trigger; // the first Flip-Flop
trigger_sync_2 <= trigger_sync_1;// the second Flip-Flop
reset_timer1 <= reset_timer;
reset_timer2 <= reset_timer1;
reset_det1 <= reset;
reset_det2 <= reset_det1;
end
// Identify the zero to one transitions on trigger signal
assign trigger_rising = trigger_sync_1 & (~trigger_sync_2);
assign trigger_falling = trigger_sync_2 & (~trigger_sync_1);
assign reset_timer3 = reset_timer1 & (~reset_timer2);
assign reset_det = reset_det2 & (~reset_det1);
// sample Mode and wb
always @(trigger_rising,trigger_falling,mode_a,mode_b,wb)
begin
if(trigger_falling == 1 || trigger_rising == 1) begin
PULSE_WIDTH = wb;
DELAY = (2*wb + 1)/2;
mode = {mode_a,mode_b};
end
end
// modes
always @(mode,reset,trigger_falling,trigger_rising,TIMER,reset,trigger,PULSE_WIDTH,DELAY,reset_det)
begin
case(mode)
2'b00: // One-Shot Mode
begin
if(reset) begin
out_low <= 0;
timer_start <= 0;
reset_timer <= 1;
end
else if(trigger_rising==1) begin
out_low <= 1;
timer_start <= 1;
reset_timer <= 1;
end
else if(TIMER>=PULSE_WIDTH) begin
out_low <= 0;
timer_start <= 0;
reset_timer <= 1;
end
end
2'b01: // Delayed Operate Mode
begin
if(reset) begin
out_low <= 0;
timer_start <= 0;
reset_timer <= 1;
end
else if(reset_det==1 && trigger==1) begin
timer_start <= 1;
reset_timer <= 0;
end
else if(trigger_rising==1) begin
timer_start <= 1;
reset_timer <= 0;
end
else if(trigger_falling==1 || trigger == 0) begin
out_low <= 0;
reset_timer <= 1;
timer_start <= 0;
end
else if(TIMER >= DELAY) begin
out_low <= 1;
timer_start <= 0;
reset_timer <= 1;
end
//else
// reset_timer <= 0;
end
2'b10: // Delayed Release Mode
begin
if(reset) begin
out_low <= 0;
timer_start <= 0;
reset_timer <= 1;
end
else if(trigger_rising==1 || trigger == 1) begin
out_low <= 1;
end
else if(trigger_falling==1 ) begin
timer_start <= 1;
reset_timer <= 0;
end
else if(TIMER>=DELAY) begin
out_low <= 0;
timer_start <= 0;
reset_timer <= 1;
end
end
2'b11: // Delayed Dual Mode
begin
if(reset) begin
out_low <= 0;
timer_start <= 0;
reset_timer <= 1;
end
else if(reset_det==1 && trigger==1) begin
timer_start <= 1;
reset_timer <= 0;
end
else if(trigger_falling==1 || trigger_rising==1 ) begin
timer_start <= 1;
reset_timer <= 0;
end
else if(TIMER>=DELAY) begin
out_low <= trigger;
timer_start <= 0;
reset_timer <= 1;
end
end
endcase
end
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// timer
always @(posedge clk or posedge timer_clear)
begin
if(timer_clear)
TIMER <= 0;
else if(timer_start)
TIMER <= TIMER + 1;
end
assign timer_clear = reset_timer3 | trigger_rising == 1 | timer_clear3 ;
assign timer_clear2 = (trigger_rising == 1)|(trigger_falling == 1);
assign timer_clear3 = timer_clear2 & (mode == 2'b11);
//delay output
always @(posedge clk)
begin
if(out_low == 1)
delay_out_n <= 0;
else
delay_out_n <= 1;
end
endmodule
延迟定时器的 Testbench Verilog 代码：
`timescale 1ns / 1ps
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// Testbench Verilog code for delay timer
module tb_ls7212;
// Inputs
reg [7:0] wb;
reg clk;
reg reset;
reg trigger;
reg mode_a;
reg mode_b;
// Outputs
wire delay_out_n;
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// Instantiate the Unit Under Test (UUT)
delay_timer_ls7212 uut (
.wb(wb),
.clk(clk),
.reset(reset),
.trigger(trigger),
.mode_a(mode_a),
.mode_b(mode_b),
.delay_out_n(delay_out_n)
);
initial begin
// Initialize Inputs
wb = 10;
mode_a = 0;
mode_b = 0;
reset = 0;
trigger = 0;
#500;
trigger = 1;
#15000;
trigger = 0;
#15000;
trigger = 1;
#2000;
trigger = 0;
#2000;
trigger = 1;
#2000;
trigger = 0;
#20000;
trigger = 1;
#30000;
trigger = 0;
#2000;
trigger = 1;
#2000;
trigger = 0;
#4000;
trigger = 1;
#10000;
reset = 1;
#10000;
reset = 0;
// Delay Operate
// Add stimulus here
end
initial begin
clk = 0;
forever #500 clk = ~clk;
end
endmodule
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Verilog 中数字延迟定时器的仿真波形
One-Shot Mode
Delayed Operate Mode
Delayed Release Mode
Delay Dual Mode
可编程延迟定时器的 Verilog 代码是可综合的，并且可以在 FPGA 上实现。
