PLZ help i m a begineer.I wanted to know in below code what will come in left nibble and right nibble say we put value #12h in the hours as shown in complete code given below .. i also wanted to know why are we ANDing it. Is it to convert HEX code 12h.

Portion i m finding difficult to understand

mov a,hrs
anl a,#0f0h
swap a
mov a,hrs
anl a,#0fh
call segdisplay
_____________________________________________________
COMPLETE PROGRAM

$MOD51
Display prog to display Hrs Min Secs 12:30:45


clk_pin_4094 bit p1.4
shift register Clock pulse
data_pin_4094 bit p1.5
shift register Data pin

SECS DATA 08H
MINS DATA 09H
HRS DATA 0aH

delayreg data 0bh
delayreg100us data 0ch
delayreg1ms data 0dh


org 0
MOV SP,#50H
mov secs,#45h ;Moves value 45 in secs
mov mins,#30h ;Moves value 30 in mins
mov hrs,#12h ;Moves value 12 in hrs

start: call displaytime
jmp start


displaytime:

clr data_pin_4094 ; make input-data-pin low
call clock_pulse
setb data_pin_4094

mov a,hrs ;hours
anl a,#0f0h
swap a
call segdisplay
mov a,hrs
anl a,#0fh
call segdisplay

mov a,mins ;minuits;
anl a,#0f0h
swap a
call segdisplay
mov a,mins
anl a,#0fh
call segdisplay

mov a,secs ;seconds
anl a,#0f0h
swap a
call segdisplay
mov a,secs
anl a,#0fh
call segdisplay

ret


clock_pulse:
setb clk_pin_4094
clr clk_pin_4094
ret
;--------------------------------------------------------
segdisplay:
mov dptr,#lookup ;now dptr=1st location of lookup table
movc a,@a+dptr ;fatches code from lookup table;gets next byte
cpl a
mov p0,a
call delay1ms
mov p0,#0ffh ;disable all segments
call clock_pulse ;to shift common of digit(FND Display)
ret


delay100us:
mov delayreg100us,#48 ;11.05mhz
djnz delayreg100us,$
ret

delay1ms:
mov delayreg1ms,#10
d1ms: call delay100us
djnz delayreg1ms,d1ms
ret
;------------------------------------------------------

lookup:
db 11111100b, 01100000b, 11011010b, 11110010b ;0 1 2 3
db 01100110b, 10110110b, 10111110b, 11100000b ;4 5 6 7
db 11111110b, 11110110b, 00010010b, 11000010b ;8 9 A b
db 01100011b, 10000110b, 00100010b, 00000010b ;C d E F

end