Jan,

the program runs correctly when adding the code i just told you,this is the only difference.

i program in KEIL C,and UART0 have high priority,

if i set the TF0&RI/TI flags manually as you said ,everything goes well,

is there any different between manually set and hardware set,you know ,the datasheet say TF0 is set&clear by hardware,TI/RI is set by harware ,clear manually

someone told me the problem occurs when bank switching is interrupt,but as I say there is only one difference.

and TO Russell Bull

i am sure it is die ,not loop because i have used DEBUG into it,when problem occurs,PC can not jump to the next command