Myself and my working partner are doing a project which scans a keypad and displays the value pressed on the keypad to a seven-segment display this is the following code we have used but it has failed to work.Any help in finding what is wrong with the code or new code would be much appreciated.
$MOD52
;-------------------------------------------------------------------------------------------
;KeysPoll.asm
;
;Keypad scan routines
;
;The polling implementation
;===========================================================================================
;UIOD connections
;output ports
;Col0 to P3.4
;Col1 to P3.5
;Col2 to P3.6
;Col3 to p3.7
;
;input ports
;Row 0 to P3.0
;Row 1 to P3.1
;Row 2 to p3.2
;Row 3 to p3.3
;-------------------------------------------------------------------------------------------
;system calls registers used
;-------------------------------------------------------------------------------------------
crlf equ 0115h ;a
delay equ 0118h ;a
display equ 011bh ;a
getchr equ 0121h ;a
inkey equ 012ah ;a
mon_return equ 0130h
print equ 0136h ;a, dptr
prthex equ 013fh ;a, r2
setintvec equ 0145h ;a, dtpr
;===========================================================================================
; Main Program
;===========================================================================================
ORG 0000h

start:
poll:
lcall KeyPressed ; see if a key is pressed
jnc poll ; repeat if no key is pressed
;--- if a key is pressed the program falls out of the loop----------------------------------
;--- the B register keeps row and column number of the--------------------------------------
;--- pressed key in its low and high nibbles, respectively. --------------------------------
lcall FindRow ; get row number
mov b, a ; save in B register
jnc Getcolumn ; continue if no error

lcall print ; else print error message
db 'Error - key row not found',0
lcall crlf

KP1:
lcall KeyPressed ; wait until key is released
jc KP1
sjmp start ; repeat

GetColumn:

lcall FindColumn ; get column number
swap a ; swap nibbles
orl a, b ; save as B register high nibble
mov b, a
jnc ReportKey ; continue if no error

lcall print ; else print error message
db 'Error - key row not found',0
lcall crlf

KP2:

lcall KeyPressed ; wait until key is released
jc KP2
sjmp start ; repeat

ReportKey:
; lcall DisplayKey ; commented out
;---show key in hex on the 7-segment display------------------------------------------------
lcall Convertkey
lcall present
mov P2, a

KP3:
lcall KeyPressed ; wait until key is released
jc KP3
ljmp start ; repeat

;===========================================================================================
;subroutine KeyPressed
;sets the carry flag if a key is pressed
;
; input : Port 3 bits are connected to a 4 by 4
; matrix type keypad. Bits P3.0 through P3.3 are
; connected to the rows, and P3.4 through P3.7 are
; connected to the columns.
;
; output : the carry flag is set if a key is pressed, else
; the carry flag is cleared.
;
; calls : nothing
; destroys : a, C
;===========================================================================================
KeyPressed:
mov P3, #0Fh ;set columns to 0, rows to 1
mov a, P3 ; read rows
orl a, #0F0H ; mask high nibble
cpl a ; a is 0 if no key is pressed
jz NoKey
setb C
ret

NoKey:
clr C
ret

;===========================================================================================
;Subroutine FindRow
;returns the row number [0 - 3] of the key pressed in the accumulator
;
; input : Port 3 bits are connected to a 4 by 4
; matrix type keypad. Bits P3.0 through P3.3 are
; connected to the rows, and P3.4 through P3.7 are
; connected to the columns.
;
; output : the row number of the key pressed is returned in a.
; the carry flag is set if a key is pressed, else
; the carry flag is cleared.
;
; calls : nothing
; destroys : a, r0 , C
;===========================================================================================
FindRow:
mov a, P3 ; read rows
mov r0, #4 ; initialize counter (R0)

TryNextRow:
rrc a ; read next row
jnc RowFound
djnz r0, TrynextRow

;--if loop FindRow does not find the row an error has occurred------------------------------
setb C ; signal an error
ret ; done

RowFound:
mov a, #4 ; number the rows
subb a, r0 ; compute row number - note C = 0
clr C ; no error
ret

;===========================================================================================
;subroutine FindColumn
;returns the column number [0 - 3] of the key pressed in the accumulator
;
; input : Port 3 bits are connected to a 4 by 4
; matrix type keypad. Bits P3.0 through P3.3 are
; connected to the rows, and P3.4 through P3.7 are
; connected to the columns.
;
; output : the row number of the key pressed is returned in a.
; the carry flag is set if a key is pressed, else
; the carry flag is cleared.
;
; calls : nothing
; destroys : a, r0, C

;===========================================================================================
FindColumn:
mov r0, #4 ; initialize counter (R0)
mov a, #0EFh ; initialize accumulator...
push acc ; ...and save on stack

TryNextColumn:
pop acc
mov P3, a
rl a
push acc
mov a, P0
orl a, #0F0h
cpl a
jnz ColumnFound
djnz r0, TryNextColumn
pop acc ; restore stack
setb C ; siganl an error
ret

ColumnFound:
pop acc ; resore stack
mov a, #4 ; number of rows
clr C ; get ready for the SUBB instruction
subb a, r0 ; compute column number
clr C ; no error

present:
inc a
movc a, @a+pc
ret
db 0c0h ;0
db 0f9h ;1
db 0a4h ;2
db 0b0h ;3
db 99h ;4
db 92h ;5
db 82h ;6
db 0f8h ;7
db 80h ;8
db 90h ;9
db 88h ;a
db 83h ;b
db 0c6h ;c
db 0a1h ;d
db 86h ;e
db 8eh ;f
;===========================================================================================
;subroutine DisplayKey
;sends a message to the host reporting the row and column
;number of the key pressed
;
; input : B register holds the column and row numbers in its
; nibbles in BCD
;
; output : a message is sent to the host
;
; calls : prthex, crlf
; destroys : a, r0, r2
;
;===========================================================================================

DisplayKey:
lcall print
db 'Key Pressed - column and row:', 0
mov a, b
lcall prthex
lcall crlf
ret

;===========================================================================================
;subroutine ConvertKey
;converts the key row and column of a 4 by 4 matrix type keypad
;to a hexadecimal number
;
; input : B register holds the column and row numbers in its
; nibbles in BCD.
;
; output : the hex number [0 - F] is returned in the accumulator.
;
; calls : nothing
; destroys : a
;
;===========================================================================================

ConvertKey:
mov a,b ; recall column and row
rl a ; make the row number the more significant
rl a ; two bits
mov C, acc.6 ; copy column number low bit to...
mov acc.0, C ; ...acc.0
mov C, acc.7 ; copy column number high bit to...
mov acc.1,C ; mask off accumulator high nibble
ret

END
Thanking you in advance
Michael Morris & Mark Moran