Below is a portion of Keypad program for 16 buttons control:

START0:
SUB_0:
MOV R3, #04H
MOV R2, #0FEH
MOV R4, #00H
SUB_1:
MOV A, R2
MOV P0, A
LCALL DELAY2
MOV A, P0
ANL A, #0F0H
CJNE A, #0F0H, SUB_2
INC R4
MOV A, R2
RL A
MOV R2, A
DJNZ R3, SUB_1
LJMP SUB_0
SUB_2:
CJNE A, #0E0H, SUB_3
MOV R6, #00H
LJMP SUB_7
SUB_3:
CJNE A, #0D0H, SUB_5
SUB_4:
MOV R6, #01H
LJMP SUB_7
SUB_5:
CJNE A, #0B0H, SUB_6
MOV R6, #02H
LJMP SUB_7
SUB_6:
CJNE A, #70H, SUB_01
MOV R6, #03H
SUB_7:
MOV A, R4
MOV DPTR, #INTIGER
MOV B, #4
MUL AB
ADD A, R6
MOVC A,@A+DPTR
MOV DYTA, A
MOV A, DYTA
SUB_01:
RET

I have doubt on how does it scan each of the 16 key and display it to LCD? #04H
MOV R2, #0FEH
MOV R4, #00H
What are those #04H, #0FEH deal with?
Could anyone please give me a hand? Thanks