lcd1602为什么不显示字符啊

上电后下载程序不显示字符调节电位器有时会出现方框然后消失，
#include<reg51.h>
#include<string.h>
#include<intrins.h>
#define uchar unsigned char
#define uint unsigned int
#define LCDIO P2
#define delay4us() _nop_();_nop_();_nop_();_nop_();
uchar buffer[6]={0};
sbit sda=P3^7;
sbit scl=P3^6;
sbit beep=P1^0;

bit flag=0,aa; //用户蹲渊义定时溢出标志位
uchar DSY_BUFFER[16]=" ";
uchar DSY_BUFFER1[16]=" ";
uchar Userpassword[6]={0};
sbit rs=P1^2;
sbit rd=P1^3;
sbit lcden=P1^4;
sbit led=P1^1;
uchar code table2[]="123456";
uchar code table[]="Your Password...";
void delayms(uint z)
{
uint x,y;
for(x=z;x>0;x--)
for(y=110;y>0;y--);
}
void delay() //短延时，两个机器周期,做总线的延时用
{;;}
void write_com(uchar com)
{
rs=0;
rd=0;
lcden=0;
P2=com;
delayms(3);
lcden=1;
delayms(3);
lcden=0;
}

void write_date(uchar date)
{
rs=1;
rd=0;
lcden=0;
P2=date;
delayms(3);
lcden=1;
delayms(3);
lcden=0;
}
void Display_String(uchar *p,uchar com)
{ uchar i;
write_com(com);
for(i=0;i<16;i++)
{
write_date(p[i]);
}
}
void init_lcd()
{
lcden=0;
write_com(0x38);
write_com(0x0c);
write_com(0x06);
write_com(0x01);
write_com(0x80);
Display_String(table,0x80);
Display_String("Lock OK! ",0xc0);
}

void start()
{
sda=1;
scl=1;
delay4us();
sda=0;
delay4us();
scl=0;
}
void stop()
{
sda=0;
scl=1;
delay4us();
sda=1;
delay4us();
scl=0;
}
void init() //初始化
{
sda=1;
delay();
scl=1;
delay();
}


void ack()
{
sda=0;
scl=1;
delay4us();
scl=0;
sda=1;
}
void noack()
{
sda=1;
scl=1;
delay4us();
scl=0;
sda=0;
}
uchar recbyte()
{
uchar i,rd;
rd=0x00;
sda=1;
for(i=0;i<8;i++)
{
scl=1;
rd<<=1;
rd|=sda;
delay4us();
scl=0;
delay4us();
}
scl=0;
delay4us();
return rd;
}
uchar sendbyte(uchar wd)
{
uchar i;
bit ack0;
for(i=0;i<8;i++)
{
sda=(bit)(wd&0x80);
_nop_();
_nop_();
scl=1;
delay4us();
scl=0;
wd<<=1;
}
delay4us();
sda=1;
scl=1;
delay4us();
ack0=!sda;
scl=0;
delay4us();
return ack0;
}
uchar Recstring(uchar slave,uchar subaddr,uchar *buffer,uchar n)
{
uchar i;
start();
if(!sendbyte(slave)) return 0;
if(!sendbyte(subaddr)) return 0;
start();
if(!sendbyte(slave+1)) return 0;
for(i=0;i<n-1;i++)
{
buffer[i]=recbyte();
ack();
}
buffer[n-1]=recbyte();
noack();
stop();
return 1;
}

uchar Sendstring(uchar slave,uchar subaddr,uchar *buffer,uchar n)
{
uchar i;
start();
if(!sendbyte(slave)) return 0;
if(!sendbyte(subaddr)) return 0;
for(i=0;i<n;i++)
{
if(!sendbyte(buffer[i])) return 0;
}
stop();
return 1;
}
void clear_password()
{ uchar i;
for(i=0;i<6;i++)
{
Userpassword[i]=' ';
}
for(i=0;i<16;i++)
{
DSY_BUFFER[i]=' ';
}
}
uchar Keys_Scan()
{
uchar temp,keynum;
P0=0x0F;
delayms(5);
temp=P0^0x0F;
switch(temp)
{
case 1:keynum=0;break;
case 2:keynum=1;break;
case 4:keynum=2;break;
case 8:keynum=3;break;
break;
}
P0=0xF0;
delayms(5);
temp=P0>>4^0x0F;
switch(temp)
{
case 1:keynum+=0;break;
case 2:keynum+=4;break;
case 4:keynum+=8;break;
case 8:keynum+=12;break;
break;
}
delayms(600);
return keynum;
}
void main()
{ uchar temp,i=0,j=0,k=0,n;
uchar IS_valid_user;
beep=1;
init();
init_lcd();
delayms(5);
aa=Sendstring(0xa0,1,table2,6);
delayms(5);
aa=Recstring(0xa0,1,buffer,6);
delayms(10);
P0=0x0f;
while(1)
{

if(P0!=0x0f)
{
temp=Keys_Scan();
switch(temp)
{
case 0: case 1: case 2: case 3: case 4:
case 5: case 6: case 7: case 8: case 9:

if (i<=5) //密码限制在6位以内
{
Userpassword[i]=temp;
DSY_BUFFER[i]='*';
Display_String(DSY_BUFFER,0xc0);
i++;
}
break;

case 10: //按A键开锁
for(k=0;k<6;k++)
{
if(buffer[k]==(Userpassword[k]+48))
flag=1;
else
flag=0;
}
if (flag==1)
{ flag=0;
i=0;
led=1; //点亮LED
clear_password();
Display_String("OPEN OK! ",0xc0);
IS_valid_user = 1;
j=0;
}
else
{
j++;
led=0; //关闭LED
clear_password();
Display_String("ERROR!Have try ",0xc0);
write_com(0xcf);
write_date(0x30+j);
IS_valid_user=0;
}
i=0;
break;

case 11: //按B键上锁
led=0;
clear_password();
Display_String(table,0x80);
Display_String("Lock OK! ",0xc0);
i=0;
IS_valid_user=0;
break;

case 12: //按C键设置新密码
//如果是合法用户则提示输入新密码
if ( !IS_valid_user)
{
i=0;
Display_String("No rights ! ",0xc0);
delayms(1000);
Display_String("Your Password...",0x80);
Display_String("Lock OK! ",0xc0);
}
else
{
i=0;
Display_String("New Password: ",0x80);
Display_String(" ",0xc0);
}

break;

case 13: //按D键保存新密码
if ( !IS_valid_user)
{ i=0;
Display_String("No rights ! ",0xc0);
delayms(1000);
Display_String("Your Password...",0x80);
Display_String("Lock OK! ",0xc0);
}
else
{i = 0;
init();
delayms(5);
for(k=0;k<6;k++)
{
Userpassword[k]=Userpassword[k]+48;
}
aa=Sendstring(0xa0,1,Userpassword,6);
delayms(5);
aa=Recstring(0xa0,1,buffer,6);
delayms(5);
clear_password();
Display_String(table,0x00);
Display_String("Password Saved! ",0xc0);
delayms(1000);
Display_String("Do lock agian ? ",0xc0);
}
break;

case 14: //按E键消除所有输入
i=0;
clear_password();
Display_String(" ",0xc0);
break;

case 15: //清除一位
if(i!=0)i--;
for(n=0;n<i;n++)
{
DSY_BUFFER1[n]='*';
}
Display_String(DSY_BUFFER1,0xc0);

}
P0=0x0f;
}
if(j==3)
{ Display_String("THIEF!!!THIEF!!!",0xc0);
j=0;
beep=0;
}
}
}