;Toggling the bits of P1 and P2 on MDE 8051 Trainer with one-sec Delay
;Tested by M. Mazidi 
;Modified from Examples in chaps 3 and 8 of 8051 Microcontroller book by Mazidis & McKinlay 
;Connect the P1 and P2 to LEDs to see the toggling. 			
 	ORG	 0
 	MOV	A,#0
 	MOV	P1,A       ;P1 as output
 	MOV	P2,A       ;P2 as output
BACK:	MOV 	A,#55H
	MOV 	P1,A
	MOV	P2,A
	ACALL	SDELAY	;one sec delay	
	MOV 	A,#0AAH
	MOV 	P1,A
	MOV	P2,A
	ACALL	SDELAY
	SJMP	BACK
;-------------------------
;One sec. delay for DS89C4x0 with MDE8051 Trainer
;XTAL=11.0592 MHz on MDE8051, 1/11.0592 MHz=90 nsec
;45 x 255 x 242 x 4 x 90 ns = 999.7 msec
;Notice DS89C4x0 uses 4 clocks for Machine Cycle. 
   			
SDELAY:
	MOV	R5, #45
H3:	MOV	R4, #242    
H2:  	MOV	R3, #255    
H1:	DJNZ	R3, H1 		
    	DJNZ	R4, H2  
    	DJNZ	R5, H3  
   	RET
;-----------------------             
	END