В данном случае PB_state присваивается после условия сам на себя. Поэтому он был не определен. PB_state это output logic. В данном случае надо еще один вход RESET заводить.
Сейчас работает нормально. Это вариант антидребезга.
`timescale 1ns / 100ps
module PushButton_Debouncer (
input wire clk,
input wire PB, // "PB" is the glitchy, asynchronous to clk, active low push-button signal
// from which we make three outputs, all synchronous to the clock
output logic PB_state, // 1 as long as the push-button is active (i.e. pushed down)
output logic PB_down, // 1 for one clock cycle when the push-button goes down (i.e. just pushed)
output logic PB_up // 1 for one clock cycle when the push-button goes up (i.e. just released)
);
initial begin
PB_state = 1'b0;
end
// First use two flip-flops to synchronize the PB signal the "clk" clock domain
logic PB_sync_0; always @(posedge clk) PB_sync_0 <= ~PB; // invert PB to make PB_sync_0 active high
logic PB_sync_1; always @(posedge clk) PB_sync_1 <= PB_sync_0;
// счетчик
logic [3:0] PB_cnt;
// When the push-button is pushed or released, we increment the counter
// The counter has to be maxed out before we decide that the push-button state has changed
wire PB_idle = (PB_state == PB_sync_1);
wire PB_cnt_max = &PB_cnt; // true when all bits of PB_cnt are 1's
always @(posedge clk)
if(PB_idle)
PB_cnt <= 0; // nothing's going on
else
begin
PB_cnt <= PB_cnt + 1'b1; // something's going on, increment the counter
if(PB_cnt_max) PB_state <= ~PB_state; // if the counter is maxed out, PB changed!
end
assign PB_down = ~PB_idle & PB_cnt_max & ~PB_state;
assign PB_up = ~PB_idle & PB_cnt_max & PB_state;
endmodule
// Тестовый модуль
module Test;
bit clk;
bit PB;
bit PB_state;
bit PB_down;
bit PB_up;
shortint i;
PushButton_Debouncer Debounce (
.clk(clk),
.PB(PB),
.PB_state(PB_state),
.PB_down(PB_down),
.PB_up(PB_up)
);
initial begin
clk = 1'b0;
PB = 1'b1;
for(i = 0; i < 8; i++) begin
#150 PB = 1'b0;
#150 PB = 1'b1;
end
#150 PB = 1'b0;
#2500 PB = 1'b1;
#2500 $stop;
end
always #50 clk = ~clk;
endmodule
