普中51单片机，数码管显示0-9，数字一直不完全显示是怎么回事。程序如下 #include<reg51.h> unsigned char Tab[]={0xc0,0xf9,0xa0,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90};unsigned int n=0,m=0; void main(){ EA=1; ET1=1; TMOD=0x20; TR1=1; TH1=(256-250); TL1=(256-250); P2=0x01; while(1){ } } void timer() interrupt 3 { n++; if(n==4000){m++;P0=~Tab[m-1]; n=0;}if(m==10)m=0;TF1=0;}