求助啊！！！！大神们帮忙吧这程序详细解释一遍被

ORG 0000H
AJMP START
ORG 0003H
CPL F0
RETI
ORG 0030H
START:MOV A,#0FFH
SETB IT0
SETB EA
SETB EX0
LOOP: JB F0, LLL
RRC A
SJMP RRR
LLL: RLC A
RRR: MOV P2,A
ACALL DTIME1
SJMP LOOP
DTIME1:MOV R7,#10
DTIME2:MOV R6,#100
DTIME3:MOV R5,#100
DJNZ R5,$
DJNZ R6,DTIME3
DJNZ R7,DTIME2
RET
END