hi;
have you tried disassembly of monitor?it should read something like this at 0bh:
ljmp 200b

while writing program assume your program starts at 2000h
org 2000h
ljmp start

org 2003
reti
org 200b
;t0 isr

start:
this is ofcourse valid if xram is located from 2000h
regards
pranav