#include "c8051f120.h"

   void Oscillator_Init()
{
    int i = 0;
    SFRPAGE   = CONFIG_PAGE;
    OSCICN    = 0x83;
    CCH0CN    &= ~0x20;
    SFRPAGE   = LEGACY_PAGE;
    FLSCL     = 0x90;
    SFRPAGE   = CONFIG_PAGE;
    CCH0CN    |= 0x20;
    PLL0CN    |= 0x01;
    PLL0DIV   = 0x01;
    PLL0FLT   = 0x21;
    PLL0MUL   = 0x02;
    for (i = 0; i < 15; i++);  // Wait 5us for initialization
    PLL0CN    |= 0x02;
    while ((PLL0CN & 0x10) == 0);
    CLKSEL    = 0x02;
}

void Port_IO_Init()
{
    // P0.0  -  Unassigned,  Push-Pull,  Digital
    // P0.1  -  Unassigned,  Push-Pull,  Digital
    // P0.2  -  Unassigned,  Push-Pull,  Digital
    // P0.3  -  Unassigned,  Push-Pull,  Digital
    // P0.4  -  Unassigned,  Push-Pull,  Digital
    // P0.5  -  Unassigned,  Push-Pull,  Digital
    // P0.6  -  Unassigned,  Push-Pull,  Digital
    // P0.7  -  Unassigned,  Push-Pull,  Digital

    // P1.0  -  Unassigned,  Open-Drain, Digital
    // P1.1  -  Unassigned,  Open-Drain, Digital
    // P1.2  -  Unassigned,  Open-Drain, Digital
    // P1.3  -  Unassigned,  Open-Drain, Digital
    // P1.4  -  Unassigned,  Open-Drain, Digital
    // P1.5  -  Unassigned,  Open-Drain, Digital
    // P1.6  -  Unassigned,  Open-Drain, Digital
    // P1.7  -  Unassigned,  Open-Drain, Digital

    // P2.0  -  Unassigned,  Open-Drain, Digital
    // P2.1  -  Unassigned,  Open-Drain, Digital
    // P2.2  -  Unassigned,  Open-Drain, Digital
    // P2.3  -  Unassigned,  Open-Drain, Digital
    // P2.4  -  Unassigned,  Open-Drain, Digital
    // P2.5  -  Unassigned,  Open-Drain, Digital
    // P2.6  -  Unassigned,  Open-Drain, Digital
    // P2.7  -  Unassigned,  Open-Drain, Digital

    // P3.0  -  Unassigned,  Open-Drain, Digital
    // P3.1  -  Unassigned,  Open-Drain, Digital
    // P3.2  -  Unassigned,  Open-Drain, Digital
    // P3.3  -  Unassigned,  Open-Drain, Digital
    // P3.4  -  Unassigned,  Open-Drain, Digital
    // P3.5  -  Unassigned,  Open-Drain, Digital
    // P3.6  -  Unassigned,  Open-Drain, Digital
    // P3.7  -  Unassigned,  Open-Drain, Digital

    SFRPAGE   = CONFIG_PAGE;
    P0MDOUT   = 0xFF;
    XBR2      = 0x40;
}

void main()
{
   int i;
   WDTCN=0xde;
   WDTCN=0xad;

  Oscillator_Init();
  Port_IO_Init();
   
  while(1)
{
       
    LOOP:P0 = 0x0f;
         for(i=0;i<=1200;i++);
         P0 = 0x0f;
             for(i=0;i<=1200;i++);
        goto LOOP;
}
  
}

这是我的代码，我想让P0口的引脚输出一个时钟信号，可是下载到板子后P0口的引脚输出一致时高电平，为什么？