but the disadvantage is that it can not be implemented for long loops
why not, here is a loop of about a day or so

MOV R7,#0
MOV R6,#0
MOV R5,#0
MOV R4,#0
MOV R3,#0
MOV R2,#0
MOV R1,#0
MOV R0,#0

LOOP: SETB FLG_WATCHDOG
JB P1.0,LOOP_END ; event has been detected
DJNZ R7,LOOP
DJNZ R6,LOOP
DJNZ R5,LOOP
DJNZ R4,LOOP
DJNZ R3,LOOP
DJNZ R2,LOOP
DJNZ R1,LOOP
DJNZ R0,LOOP
MOV A,#NO_EVENT
JMP HARDWARE_FAILURE
LOOP_END: Erik