XL2000 8051 development board experiment 1 lights blinking and assembly code explained

org 0000h ;start
ajmp LOOP; jump to LOOP label
org 0080h; get to 0030h to reserve some space
LOOP:
mov p1,#0ffh; turn off all lights
clr p1.0 ;turn on light at p1.0
lcall delay ;delay for a while
clr p1.1 ;turn on light at p1.1
lcall delay
clr p1.2 ;
lcall delay
clr p1.3 ;
lcall delay
clr p1.4 ;
lcall delay
clr p1.5 ;
lcall delay
clr p1.6 ;
lcall delay
clr p1.7 ;
lcall delay
AJMP LOOP; jump to LOOP and restart to run
delay: mov r5,#20 ; delay number。
d1: mov r6,#40
d2: mov r7,#248
djnz r7,$
djnz r6,d2
djnz r5,d1
ret
end