单片机时钟程序，分钟总是到60，求帮助 -

#include <reg51.h>
sbit key1 = P1^0;
sbit beep = P1^0;
bit flag1s = 0;
bit KeySta = 1;
unsigned char hour = 12;
unsigned char minute =59;
unsigned char second =50;
unsigned char mode = 0;
void FreshTime();
void TimeInit();
void IntInit();
void InitLedBuff();
void keyscan();
void zhengdian();
unsigned char code LedChar[] = {0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,
0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71,0x40,0x00};//共阴数码管显示字符转换表
unsigned char LedBuff[6] = {0xff,0xff,0xff,0xff,0xff,0xff};//数码管显示缓冲区
void main()
{
TimeInit();
IntInit();
InitLedBuff();
while(1)//显示内容处理
{
if(flag1s&&!mode) //时间显示模式
{
flag1s = 0;
FreshTime();
}
else if(mode == 1) //校准分钟
{
LedBuff[0] = 17;
LedBuff[1] = 17;
LedBuff[4] = 17;
LedBuff[5] = 17;//不显示
LedBuff[2] = minute/10;
LedBuff[3] = minute%10;
}
else if(mode == 2) //校准小时
{
LedBuff[2] = 17;
LedBuff[3] = 17;
LedBuff[4] = 17;
LedBuff[5] = 17;//不显示
LedBuff[0] = hour/10;
LedBuff[1] = hour%10;
}
else if(mode == 3) //校准完成重新显示
{
InitLedBuff();
mode = 0;
}
keyscan();
}
}
void InitLedBuff()//初始化时间到显示缓冲区
{
LedBuff[0] = hour/10;
LedBuff[1] = hour%10;
LedBuff[2] = minute/10;
LedBuff[3] = minute%10;
LedBuff[4] = second/10;
LedBuff[5] = second%10;
}
void FreshTime()//刷新时间到显示缓冲区
{
second++;
if(second == 60)//进位
{
second = 0;
minute++;
LedBuff[2] = minute/10;
LedBuff[3] = minute%10;
if(minute ==60)//进位
minute = 00;
hour++;
if(hour == 24)
hour = 0;
LedBuff[0] = hour/10;
LedBuff[1] = hour%10;
}
LedBuff[4] = second/10;
LedBuff[5] = second%10;
}
void TimeInit()//定时器初始化
{
TMOD = 0X11; //设置定时器为模式1
TL0 = 0xB0;
TH0 = 0x3C; //定时初值 50ms
TL1 = 0x18; //
TH1 = 0xFC; //定时初值 1ms
TR0 = 1; //定时器0开始计时
TR1 = 1; //定时器1开始计时
ET1 = 1; //使能定时器1
ET0 = 1; //使能定时器0
PT0 = 1; //提高计时准确性，提高定时器0中断优先级
EA = 1; //打开总中断
}
void IntInit()//外部中断初始化
{
IT0 = 1; //下降沿触发
EX0 = 1; //使能外部中断0
}
void keyscan() //按键扫描及处理
{
static bit backup = 1;
if (KeySta != backup) //当前值与前次值不相等说明此时按键有动作
{
if (backup == 0) //如果前次值为0，则说明当前是弹起动作
{
if(mode == 1)
{
minute++;
if(minute==60)
minute = 0;
}
else if(mode == 2)
{
hour++;
if(hour==24)
hour = 0;
}
}
backup = KeySta; //更新备份为当前值，以备进行下次比较
}
}
void Int0() interrupt 0
{
mode++;
if(mode == 4)
{
mode = 0;
}
}
void Ledfresh() //数码管显示刷新
{
static unsigned char i = 0;
switch(i)
{
case 0 : P2 = ~(0x01<<i);P0 = LedChar[LedBuff[i]];i++;break;
case 1 : P2 = ~(0x01<<i);P0 = LedChar[LedBuff[i]];i++;break;
case 2 : P2 = ~(0x01<<i);P0 = LedChar[LedBuff[i]];i++;break;
case 3 : P2 = ~(0x01<<i);P0 = LedChar[LedBuff[i]];i++;break;
case 4 : P2 = ~(0x01<<i);P0 = LedChar[LedBuff[i]];i++;break;
case 5 : P2 = ~(0x01<<i);P0 = LedChar[LedBuff[i]];i=0;break;
}
}
void Time0() interrupt 1 //12MHz 50ms
{
static unsigned char n = 0;
TL0 = 0xB0;
TH0 = 0x3C;
n++;
if(n==20)
{
n=0;
flag1s = 1;//1s标志位
}
}
void zhengdian() //整点报时
{
if((second==0)&&((minute==0)&&(hour>=0)))
{
beep=1;
beep=0;
}
}
void Time1() interrupt 3 //12MHz 1ms
{
static unsigned char keybuff = 0xff;
TL1 = 0x18;
TH1 = 0xFC;
Ledfresh();
keybuff = (keybuff<<1)|key1;
if (keybuff == 0x00)
{
KeySta = 0;
}
else if (keybuff == 0xFF)
{
KeySta = 1;
}
else
{}
}

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