I have read a book telling me that the interupt address of timer0 is 0BH while timer1 is 1BH.

By referring the following code, I would like to know the use of the interupt address.
I didn't find the program use it. Beside, is it abirtary to assign the address for the Timer subroutine? (i.e. ORG 6BH)

And why in the START subroutine, the SP has to be assign the value of #60H? can I put other value between #30H and #7FH?

Finally, I would like to know the last command in the program: SJUP $
What is the meaning of $, which register is it referring to?

; ------ DEFINE LOCATION OF MAIN LOOP AND INTERRUPT SUBROUTINE ------
ORG 00H
SJMP START
ORG 6BH
AJMP TIMER0

; ------ MAIN LOOP START ------
START: MOV SP, #60H
MOV R0, #100
MOV R1, #FFH
SETB EA ;ENABLE INTERRUPT
SETB ET0 ;ENABLE TIMER 0 INTERRUPT
MOV TMOD, #0 ;SET THE TIMER 0 TO MODE 0
MOV TH0, #63H ;INITIALIZE THE TIMER
MOV TL0, #18H
SETB TR0 ;START THE TIMER
MOV P1, #AAH
SJMP $

Thnx...
Sunny CHU