单项选择题

在步进电机细分控制器中，以下程序所起的作用为（    ）
always@(posedge clk or negedge rst)
begin
     if(!rst)
         begin
               counta_h<=0;
               counta_l<=0;
               pos_pxa_clk<=0;
               neg_pxa_clk<=0;
         end
     else
         begin
             if(pxa==1)
               begin
                   counta_h<=counta_h+1;
                   counta_l<=0;
                   if(counta_h==1)
                       pos_pxa_clk<=1;
                  else
                       pos_pxa_clk<=0;
               end
......
A、边沿检测模块
B、正弦波发生模块
C、三角载波发生模块
D、 比较模块

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