hi every one i have made a simulation of akeyboard using AT89C51 microcontroller but the problem is whenever i connect the columns of the keyboard to port 2 the keyboard doesnot work i tried connecting the columns to port P0 with out connecting apull up resistor to the port and it worked great so any one tell what is wrong with it
thise is the program i made (assembly) using keil and the simulation using isis

...insert code hereORG 00H
MOV P,#0FFH                     ;make port 0 input
K1: MOV P1,#0                   ;ground all rows
MOV A,P2                        ;read all columns check if all keys open
ANL A,#00001111B                ;mask lower four bits
CJNE A,#00001111B,K1            ;check till all keys are released
K2: ACALL DELAY                 ;wait for debounce
MOV A,P2                        ;read columns
ANL A,#00001111B                ;mask
CJNE A,#00001111B,OVER          ;see if any key pressed
SJMP K2                         ;no key pressed
OVER: ACALL DELAY               ;wait for debounce
MOV A,P2                        ;read all columns 
ANL A,#00001111B                ;mask
CJNE A,#00001111B,OVER1         ;see if any key pressed
SJMP K2                         ;no key pressed
OVER1: MOV P1,#11111110B        ;ground first row
MOV A,P2                        ;read columns
ANL A,#00001111B                ;mask lower four bits
CJNE A,#00001111B,ROW_0         ;check if any key pressed
MOV P1,#11111101B               ;no key pressed check second row
MOV A,P2                        
ANL A,#00001111B
CJNE A,#00001111B,ROW_1           
MOV P1,#11111011B                ;no key pressed check third row
MOV A,P2
ANL A,#00001111B
CJNE A,#00001111B,ROW_2
MOV P1,#11110111B                 ;no key pressed check fourth row
MOV A,P2                          
ANL A,#00001111B
CJNE A,#00001111B,ROW_3
LJMP K2                          ;do it again
ROW_0: MOV DPTR,#KCODE0          ;load key row 0
SJMP FIND                        ;find which one is pressed
ROW_1: MOV DPTR,#KCODE1          ;load key row 1
SJMP FIND                        ;find which one is pressed
ROW_2: MOV DPTR,#KCODE2          ;load key row 2
SJMP FIND                        ;find which key is pressed
ROW_3: MOV DPTR,#KCODE3          ;load key row 3
FIND: RRC A
JNC MATCH
INC DPTR
SJMP FIND
MATCH: CLR A                     ;if key is grounded then thise the key pressed
MOVC A,@A+DPTR
MOV P3,A                         ;move ascii code for the pressed key
LJMP K1                          ;do it infintely                    
ORG 300H
KCODE0: DB '0','1','2','3'	 ;ROW 0
KCODE1: DB '4','5','6','7'   ;ROW 1
KCODE2: DB '8','9','A','B'   ;ROW 2
KCODE3: DB 'C','D','E','F'   ;ROW 3
DELAY: MOV TMOD,#01H                 ;thise is the delay subroutine
MOV TL0,#0FFH
MOV TH0,#0B7H
SETB TR0
WAIT: JNB TF0,WAIT
CLR TR0
CLR TF0
RET
END