普中HC-6800单片机静态数码管显示出错，原因及如何改进

#include <REGX52.H>

unsigned char NixieTable[] = {0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F};    // 0~9对应位选端口，A~F为0x77,0x7C,0x39,0x5E,0x79,0x71;0x00为空

// 控制数码管显示的函数
void Nixie(unsigned char Location, unsigned char Number)
{
    switch(Location)
    {
        case 1: 
            P1_0 = 0; 
            P1_1 = 0; 
            P1_2 = 0; 
            P1_3 = 1; 
            break;  // 将选定位选端口1
        case 2: 
            P1_0 = 0; 
            P1_1 = 0; 
            P1_2 = 1; 
            P1_3 = 0; 
            break;  // 将选定位选端口2
        case 3: 
            P1_0 = 0; 
            P1_1 = 1; 
            P1_2 = 0; 
            P1_3 = 0; 
            break;  // 将选定位选端口3
        case 4: 
            P1_0 = 1; 
            P1_1 = 0; 
            P1_2 = 0; 
            P1_3 = 0; 
            break;  // 将选定位选端口4
    }
    P0 = NixieTable[Number];  // 在数码管上显示指定数字
}

void main()
{
    while(1)
    {
        Nixie(4, 6);  // 将数字6显示在数码管的第4位
    }
}