;Displaying "YES" on LCD using 4-bit data line
;Written and tested by Mazidi 
;Modified from prog 12-1 of 8051 Microcontroller book by Mazidis & McKinlay 
;P1.7-P1.4 to D7-D4 of LCD
;P2.0=RS, P2.1=R/W, and P2.2=E
;You can modify this program to use only a single PORT P1
;To initialize the LCD 4-bit data option we must send values 33H, 32H and 28H as command 			
 			ORG	 0
 			ACALL	DELAY 
 			ACALL	DELAY 
 			MOV	A,#33H		;needed by LCD 4-bit data option	
			ACALL	COMNWRT4    	
			ACALL	DELAY  
			MOV	A,#32H		;needed by LCD 4-bit data option
			ACALL	COMNWRT4    	
			ACALL	DELAY
			MOV	A,#28H		;needed by LCD 4-bit data option
			ACALL	COMNWRT4    	
			ACALL	DELAY        	
			MOV	A,#0EH     	
			ACALL	COMNWRT4		
			ACALL	DELAY		
			MOV	A,#01     	
			ACALL	COMNWRT4    	
			ACALL	DELAY		
			MOV	A,#06H     	
			ACALL	COMNWRT4    	
			ACALL	DELAY		
			MOV	A,#84H     	
			ACALL	COMNWRT4    	
			ACALL	DELAY		
			MOV	A,#'Y'     	
			ACALL	DATAWRT4    	
			ACALL	DELAY		
			MOV	A,#'A'     	
			;ACALL	DATAWRT4
			;MOV	A,#'S'     	
			ACALL	DATAWRT4    	
			ACALL	DELAY	  		
AGAIN:			SJMP	AGAIN 

;-----------------Command-Write 4-bit version     	
COMNWRT4:                   	
			MOV	R1,A		;save a copy
			ANL	A,#0F0H		;mask the lower 4-bits
			MOV     P1,A       	;issue it to LCD data bus
			CLR	P2.0       	
			CLR	P2.1       	
			SETB	P2.2       	
			ACALL	DELAY		
			CLR	P2.2
			MOV	A,R1		;get a copy
			ANL	A,#0FH		;mask the upper 4-bit
			RL	A		;shift it to left 4 times
			RL	A
			RL	A
			RL	A
			MOV     P1,A       	;issue it to LCD data bus
			CLR	P2.0       	
			CLR	P2.1       	
			SETB	P2.2       	
			ACALL	DELAY		
			CLR	P2.2
 	
			RET

;-----------Data-Write 4-bit version  
DATAWRT4:                   	
			MOV	R1,A		;save a copy
			ANL	A,#0F0H		;mask the lower 4-bits
			MOV	P1,A       	;issue it to LCD data bus
			SETB	P2.0       	
			CLR	P2.1       	
			SETB	P2.2       	
			ACALL	DELAY		
			CLR	P2.2
			MOV	A,R1		;get a copy
			ANL	A,#0FH		;mask the upper 4-bit
			RL	A		;shift it to left 4 times
			RL	A
			RL	A
			RL	A
			MOV     P1,A       	;issue it to LCD data bus	
			SETB	P2.0       	
			CLR	P2.1       	
			SETB	P2.2       	
			ACALL	DELAY		
			CLR	P2.2
       	
			RET
			
;-------------------------
;200 msec. delay for DS89C4x0 with MDE8051 Trainer
;XTAL=11.0592 MHz on MDE8051
;9 x 255 x 242 x 4 x 90 ns = 199 msec
;Notice DS89C4x0 uses 4 clocks for Machine Cycle. 
   			
DELAY:
		MOV	 R5, #9
H3:		MOV	 R4, #242    
H2:  		MOV	 R3, #255    
H1:	 	DJNZ	 R3, H1 		
    		DJNZ	 R4, H2  
    		DJNZ	 R5, H3  
   		RET             
		   END