Using four digit LED display
In this example all four displays, instead of two, are active so that
it is possible to write numbers from 0 to 9999. Here, the number 1 234
is displayed. After initialization, the program remains in the loop LOOP
where digital multiplexing is performed. The subroutine Disp is used to
convert binary numbers into corresponding combinations of bits for the
purpose of activating display lighting segments.
;************************************************************************
;* PROGRAM NAME : 7Seg5.ASM
;* DESCRIPTION : Program displays number"1234" on 7-segment LED display
;************************************************************************
;BASIC DIRECTIVES
$MOD53
$TITLE(7SEG5.ASM)
$PAGEWIDTH(132)
$DEBUG
$OBJECT
$NOPAGING
;STACK
DSEG AT 03FH
STACK_START: DS 040H
;RESET VECTORS
CSEG AT 0
JMP XRESET ; Reset vector
ORG 100H
XRESET: MOV SP,#STACK_START ; Define Stack pointer
LOOP: MOV P1,#0 ; Turn off all display segments
MOV P3,#20h ; Activate display D4
MOV A,#04 ; Write digit 4 on display D4
LCALL Disp ; Find mask for that digit
MOV P1,A ; Put the mask on the port
MOV P1,#0 ; Turn off all display segments
MOV P3,#10h ; Activate display D3
MOV A,#03 ; Write digit 3 on display D3
LCALL Disp ; Find mask for that digit
MOV P1,A ; Put the mask on the port
MOV P1,#0 ; Turn off all display segments
MOV P3,#08h ; Activate display D2
MOV A,#02 ; Write digit 2 on display D2
LCALL Disp ; Find mask for that digit
MOV P1,A ; Put the mask on the port
MOV P1,#0 ; Turn off all display segments
MOV P3,#04h ; Activate display D1
MOV A,#01 ; Write digit 1 on display D1
LCALL Disp ; Find mask for that digit
MOV P1,A ; Put the mask on the port
SJMP LOOP ; Return to the lable LOOP
Disp: ; Subroutine for writing digits
INC A
MOVC A,@A+PC
RET
DB 3FH ; Digit 0 mask
DB 06H ; Digit 1 mask
DB 5BH ; Digit 2 mask
DB 4FH ; Digit 3 mask
DB 66H ; Digit 4 mask
DB 6DH ; Digit 5 mask
DB 7DH ; Digit 6 mask
DB 07H ; Digit 7 mask
DB 7FH ; Digit 8 mask
DB 6FH ; Digit 9 mask
END ; End of program
