INT_HIGHPRI:
PUSH PSW
PUSH ACC
MOV TH0,#HIGH -TID0
MOV A,TL0 ADD A,#(LOW -TID0) + ADJ
MOV TL0,A 
PUSH INT_LOWPRI_LO
PUSH INT_LOWPRI_HI  ; or was that HI, LO?
RETI ; Jump to INT_LOWPRI, drop interrupt flag.

INT_LOWPRI:  ; You should earlier store the address of this in RAM under INT_LOWPRI_LO,_HI 

; Everything here happens on main program priority level (all other interrupts may kick in)
; Increment your 0.01s counter
; Check if ==100, increment seconds, reset
; Perform time calculation, update display
; Perform all the other RTC-related operations you want

POP ACC
POP PSW
RET ; return from the interrupt...