DS12C887时钟不走的原因有哪些？

#include<reg52.h>
#define uchar unsigned char
#define uint unsigned int
sbit dula=P2^6;
sbit wela=P2^7;
sbit rs=P3^5;
sbit lcden=P3^4;
sbit s1=P3^0;
sbit s2=P3^1;
sbit s3=P3^2;
sbit rd=P3^7;
sbit dscs=P1^4;
sbit dsas=P1^5;
sbit dsrw=P1^6;
sbit dsds=P1^7;
void write_ds(uchar,uchar);
uchar read_ds(uchar);
void set_time();
char miao,shi,fen;
uchar code table[]=" 2007-7-30 MON";
uchar code table1[]=" : : ";
void delay(uint z)
{
uint x,y;
for(x=z;x>0;x--)
for(y=110;y>0;y--);
}
void set_time()
{
write_ds(4,10);
write_ds(2,32);
write_ds(0,00);
}
void write_com(uchar com)
{
rs=0;
lcden=0;
P0=com;
delay(5);
lcden=1;
delay(5);
lcden=0;
}
void write_date(uchar date)
{
rs=1;
lcden=0;
P0=date;
delay(5);
lcden=1;
delay(5);
lcden=0;
}
void init()
{
uchar num;
set_time();
dula=0;
wela=0;
lcden=0;
write_com(0x38);
write_com(0x0c);
write_com(0x06);
write_com(0x01);
write_com(0x80);
for(num=0;num<15;num++)
{
write_date(table[num]);
delay(5);
}
write_com(0x80+0x40);
for(num=0;num<12;num++)
{
write_date(table1[num]);
delay(5);
}
}
void write_sfm(uchar add,uchar date)
{
uchar shi,ge;
shi=date/10;
ge=date%10;
write_com(0x80+0x40+add);
write_date(0x30+shi);
write_date(0x30+ge);
}
void write_ds(uchar add,uchar date)
{
dscs=0;
dsas=1;
dsds=1;
dsrw=1;
P0=add;
dsas=0;
dsrw=0;
P0=date;
dsrw=1;
dsas=1;
dscs=1;
}
uchar read_ds(uchar add)
{
uchar ds_date;
dsas=1;
dsds=1;
dsrw=1;
dscs=0;
P0=add;
dsas=0;
dsds=0;
P0=0xff;
ds_date=P0;
dsds=1;
dsas=1;
dscs=1;
return ds_date;
}
void main()
{
init();
while(1)
{
miao=read_ds(0);
fen=read_ds(2);
shi=read_ds(4);
write_sfm(10,miao);
write_sfm(7,fen);
write_sfm(4,shi);
}
}

这是代码

（0xa,0x20）0x0a是寄存器A的地址 0x20是打开振荡器