PIC16F877a需要读取特定的波形图案

受到警告

设置CCP模块在每一个上升沿捕获。允许中断发生。在ISR存储器中，CCPRX寄存器的值在一对辅助寄存器中，然后将CCP模块设置为在每个下降沿上捕获。它会产生另一个中断。这一次，你必须计算CCPRX寄存器的新值与存储在辅助寄存器中的旧值之间的差值。计算值乘以Ty-WIL给出信号停留在高电平的时间。因此，您可以确定比特值是0还是1。



      以下为原文

    Set the CCP module to capture on every rising edge. Allow for interrupts to occur. At the ISR store the value of the CCPRx register in a pair of auxiliary registers, then set the CCP module to capture on every falling edge. It will generate another interrupt. This time you have to calculate the difference between the new value of the CCPRx registers and the old value stored in the auxiliary registers. The calculated value multiplied by TCy wil give the time the signal stayed at the high level. So you can determine if the bit value is 0 or 1.

你也可以使用两个CCP模块，一组在上升时触发，一个在下降。在从下降沿CCP中断（不使用上升沿上的Its）之后，计算两个捕获的计时器读数从CCP寄存器中的差值，即脉冲宽度（在定时器时钟周期中）。



      以下为原文

    You can also use two CCP modules, one set to trigger on the rise and one on the fall. After the interrupt from the falling edge CCP (do not use ints on rising edge) then calculate the difference in the two captured timer readings from the CCP registers and that is the pulse width (in timer clock cycles).

这也可以用外部中断来完成。



      以下为原文

   
This can also be done with the external interrupt.