有关系统时钟和PWM工作频率在30Hz怎么设置以及有什么区别吗

module breath_led
#(
parameter CNT_1US_MAX = 6'd49 ,
parameter CNT_1MS_MAX = 10'd999 ,
parameter CNT_1S_MAX = 10'd999
)
(
input wire sys_clk , //系统时钟50MHz
input wire sys_rst_n , //全局复位

 output reg led_out //输出信号，控制led灯
 );

 ////
 //\* Parameter and Internal Signal \//
 ////
 //reg define
 reg [5:0] cnt_1us ;
 reg [9:0] cnt_1ms ;
 reg [9:0] cnt_1s ;
 reg cnt_1s_en ;

 ///
 //\* Main Code \//
 ////
 //cnt_1us:1us计数器
 always@(posedge sys_clk or negedge sys_rst_n)
 if(sys_rst_n == 1'b0)
 cnt_1us <= 6'b0;
 else if(cnt_1us == CNT_1US_MAX)
 cnt_1us <= 6'b0;
 else
 cnt_1us <= cnt_1us + 1'b1;

 //cnt_1ms:1ms计数器
 always@(posedge sys_clk or negedge sys_rst_n)
 if(sys_rst_n == 1'b0)
 cnt_1ms <= 10'b0;
 else if(cnt_1ms == CNT_1MS_MAX && cnt_1us == CNT_1US_MAX)
 cnt_1ms <= 10'b0;
 else if(cnt_1us == CNT_1US_MAX)
 cnt_1ms <= cnt_1ms + 1'b1;

 //cnt_1s:1s计数器
 always@(posedge sys_clk or negedge sys_rst_n)
 if(sys_rst_n == 1'b0)
 cnt_1s <= 10'b0;
 else if(cnt_1s == CNT_1S_MAX && cnt_1ms == CNT_1MS_MAX
 && cnt_1us == CNT_1US_MAX)
 cnt_1s <= 10'b0;
 else if(cnt_1ms == CNT_1MS_MAX && cnt_1us == CNT_1US_MAX)
 cnt_1s <= cnt_1s + 1'b1;

 //cnt_1s_en:1s计数器标志信号
 always@(posedge sys_clk or negedge sys_rst_n)
 if(sys_rst_n == 1'b0)
 cnt_1s_en <= 1'b0;
 else if(cnt_1s == CNT_1S_MAX && cnt_1ms == CNT_1MS_MAX
 && cnt_1us == CNT_1US_MAX)
 cnt_1s_en <= ~cnt_1s_en;

 //led_out:输出信号连接到外部的led灯
 always@(posedge sys_clk or negedge sys_rst_n)
 if(sys_rst_n == 1'b0)
 led_out <= 1'b0;
 else if((cnt_1s_en == 1'b1 && cnt_1ms  cnt_1s))
 led_out <= 1'b0;
 else
 led_out <= 1'b1;

 endmodule