51 single chip microcomputer timer 0 affect the normal work of the timer 1, how to solve?-CodePudding

expected effect:
On the PC with serial debugging assistant send microcontroller one character at a time, single-chip microcomputer automatically send a "123" to the PC,

code:

 # include 

Unsigned char flag, a; 

Void main () 
{
TMOD=0 x21; 
TH1=0 XFD; 
TL1=0 XFD; 
TH0=0 xfe; 
TL0=0 x33; 
TR1=1; 
REN=1; 
SM0=0; 
The SM1=1; 
EA=1; 
ES=1; 
ET0=1; 
TR0=1; 

While (1) 
{
If (flag==1) 
{
ES=0; 
flag=0; 
SBUF='1'. 
while(! TI); 
TI=0; 
SBUF='2'. 
while(! TI); 
TI=0; 
SBUF='3'; 
while(! TI); 
TI=0; 
ES=1; 
} 
} 
} 

Void ser () interrupt 4 
{
RI=0; 
A=SBUF; 
flag=1; 
}

problem phenomenon:
After power on, PC haven't send any character, single-chip computer began to constantly send "123" to the PC,
But if the ET0=1; Or TR0=1; Code (18 ~ 19) statement annotations, can work normally,

if you can help solve, thank you very much!