MOV A, R1
   SUBB A, #01H               
   ;DA A                      
   MOV R1, A
   CJNE R1, #000H, END_T0_INT   ; Check if 1 min has passed. 
   MOV R1, #59H                 ; Reset Seconds to 59
   MOV A, R2
   SUBB A, #01H                 
   ;DA A                         
   MOV R2, A
   CJNE R2, #060H, END_T0_INT