This code is modified from the question "How can I use a timer to count 5 seconds?" in FAQ. I expect to get p1.5 blinking time change when I change th0 and tl0 but not.

Thanks for reply

TCOUNT EQU 40h ;This is an address in IRAM
ALARM EQU 00h ;This is an address of BIT memory
TIH equ 00h
TIL equ 0ffh

ORG 0000h
LJMP MAIN

ORG 000Bh
T0_INTERRUPT:
CLR tr0
MOV TL0,#til ;Set TL0 to 0B0h
MOV TH0,#tih ;Set TH0 to 3Ch
setb tr0
jb p1.5,cc
setb p1.5
sjmp ccc
cc: clr p1.5
ccc:

T0_EXIT:
RETI ;Return from the interrupt


MAIN:
MOV TMOD,#01h ;Set timer 0 to 16-bit mode
MOV TH0,#tih ;Initialize TH0 to overflow every .05 seconds
MOV TL0,#til ;Initialize TL0 to overflow every .05 seconds
SETB ET0 ;Enable timer interrupt 0
SETB EA ;Enable all interrupts

MOV TCOUNT,#20 ;Set TCOUNT to 20 to wait for 1 second
SETB TR0 ;Turn timer 0 on
sjmp $