INCLUDE 89C51.MC
;-------------------4 Digit 7-Segments ---------------------
; Microcontroller connections to DAC0808
DATA		EQU	P0		; data lines P0-P3

D1		EQU	P0.4		; display 1
D2		EQU	P0.5		; display 2
D3		EQU 	P0.6		; display 3
D4		EQU	P0.7		; display 4
;----------------------------------------------------------
; Register definitions.

BUF1		EQU	00h		; first two digits
BUF2		EQU	01h		; last two digits
;----------------------------------------------------------
(0000H):
		JMP on_reset
;-----------------------Timer-0 intrrupt-------------------
(000BH): 		
		CALL display	; display
		CLR TF0
RETI
;----------------------------------------------------------
(00FFH):
on_reset:
;Initialize interrupt
		MOV DATA,#00H	; display in off state
		MOV IE,#82H		; timer-0 interrupt enable
		MOV TMOD,#09H	; timer-0 16-bit mode
		MOV TH0,ECH		; 5msec delay at 12MHz
		MOV TL0,78H
		SETB D4		; turn on digiT-4
		SETB TCON.4		; timer running
ENDLESS:
		MOV BUF1,#12H	; 12 on display
		MOV BUF2,#34H	; 34 on display
		JMP ENDLESS	
;----------------------------------------------------------
display:
;destroy A
		JB D4,DISP1
		JB D3,DISP4
		JB D2,DISP3
		JB D1,DISP2
DISP1:
		CLR D4
		MOV A,BUF1		; digit 1 display
		ANL A,#0FH
		MOV DATA,A
		SETB D1
DISP2:		
		CLR D1
		MOV A,BUF1		; digit 2 display
		ANL A,#F0H
		RR A
		RR A
		RR A
		RR A
		MOV DATA,A
		SETB D2
DISP3:		
		CLR D2
		MOV A,BUF2		; digit 3 display
		ANL A,#0FH
		MOV DATA,A
		SETB D3
DISP4:		
		CLR D3
		MOV A,BUF2		; digit 4 display
		ANL A,#F0H
		RR A
		RR A
		RR A
		RR A
		MOV DATA,A
		SETB D4
RET
;----------------------------------------------------------