hai sunny

before ur main just put one more ORG and that will solve the problem.

ORG 23H
AJMP MAIN

ORG 03H
AJMP TIMER

ORG 300H ------> new ORG
TIMER:
-------> write ur timer module code here
RETI

MAIN:
-------> write ur main module code here
END

for timer0 the interrupt vector os 000Bh and not 0003h. chk it again

good luck
-sathish