为什么使用内部FRC时pic32不能在80兆赫下运行

嗨，我设计了一个PCB板与PIC32 MX795F512L。我想运行它在80兆赫与内部FRC PLL。但它不运行在80兆赫。我有一个Explorer 16板，可以运行完全相同的代码在80兆赫，但我的PCB不运行。此外，我的PCB可以在40 MHz或更少的情况下运行相同的代码，而不是80。我把所有必要的电容放在电路内6毫米之内。我已经检查了PIC32与板的连接，它们也很好。这是我的配置设置。这个设置是运行PIC32在80兆赫内FRC。因此，当我改变FPLLoDIV= DIVIG2时，PIC32开始运行。但是当FPLLoDIV= DIVIG1时它不运行。令人惊讶的是，在40MHz或更低频率下，一切都运行良好，所以电路设计或硬件似乎不是问题，但当我焊接另一个全新的完全相同的PCB时，它工作得很好。因为这个问题，我现在浪费了3个PCB。有人能帮我理解吗？



      以下为原文

    Hi, I have designed a PCB board with PIC32MX795F512L. I want to run it at 80 MHz with Internal FRC PLL. But It doesn't run at 80 MHz. I have a Explorer 16 Board which can run the Exact same code at 80 MHz but my PCB doesn't run. Also, My PCB can run this same code at 40 MHz or less but not 80. I have all the necessary capacitors placed within 6 mm in the circuit. I have checked the connections of the PIC32 with board and they are also fine. Here is my config settings.

#pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1, FWDTEN = OFF
#pragma config POSCMOD = HS, FNOSC = FRCPLL, FPBDIV = DIV_1
#define SYS_FREQ (80000000L)


This Settings is to run PIC32 at 80 MHz on Internal FRC. So, when I change FPLLODIV = DIV_2 PIC32 starts running. but It doesn't run when FPLLODIV = DIV_1. Surprisingly, everything runs fine at 40 MHz or less so circuit design or hardware does not seem to be the problem but when I soldered another all new  exact same PCB, It worked fine. I have wasted 3 PCB by now because of this problem. can anyone help me understand it?