$NOSYMBOLS  				;  ohne Symboltabelle im Listing
$NOMOD51				;  8051-Modus ausschalten
$INCLUDE (REG509.INC)			;  Einbinden der Registernamen des C509

	

	MOV P5,#00
	MOV R6,#06

;---------------------------------------------------------------------------------------------------

start:

	CALL startc
	MOV A,#11010000b 	;Slaveadresse DS1307	
	CALL send
	MOV A,#00H 		;Registeradresse
	CALL send
	MOV A,#00000101b 	;Daten
	CALL send
	CALL stop
	
	CALL startc
	MOV A,#11010000b
	CALL send
	MOV A,#07H
	CALL send
	MOV A,#10010000b
	CALL send
	CALL stop
	
back_1:	CALL startc		;Stackpointer wird auf Register 00h gesetzt
	MOV A,#11010000b
	CALL send
	MOV A,#00H
	CALL send 
	CALL stop

back_2:	CALL startc			 
	MOV A,#11010001b
	CALL send
	CALL recv
	CALL stop

	MOV P5,A
	JMP back_1		;Leseschlaufe des Registers 00h		



;************************************************************************
;		I2C PROTOCOL LIBRARY
;************************************************************************

;************************************************************************
;		Ports Used for I2C Communication
;************************************************************************

	sda equ P1.7
	scl equ P1.6

;************************************************************************
;		Start Condition for I2C Communication
;************************************************************************

startc:         
        clr scl 
        setb sda 
        nop 
        nop 
        setb scl 
        nop 
        nop 
        clr sda 
        ret 

;************************************************************************
;		Stop Condition For I2C Bus
;************************************************************************

stop: 
        nop 
        nop 
        clr sda 
        setb scl 
        nop 
        nop 
        setb sda 
        nop 
        nop 
        clr scl 
        ret 


;************************************************************************
;		Sending Data to slave on I2C bus
;		       with Acknowledgement
;************************************************************************

send:
	mov r7,#8

back:	
	clr scl
	nop
	nop
	nop
	rlc a
	mov sda,c
	setb scl
	nop
	nop
	nop
	clr scl
	nop
	nop
	nop
	djnz r7,back
	clr sda
	setb scl
	nop
	nop
	nop
	nop
	clr scl
	nop
	nop
	nop
	ret

;************************************************************************
;		Receiving Data from slave on I2C bus
;		       with Acknowledgement
;************************************************************************

	
recv: 
        mov r7,#08 
back2: 
        setb sda 
        setb scl 
        nop 
        nop 
        nop 
        mov c,sda 
        rlc a 
        clr scl 
        nop 
        nop 
        nop 
        djnz r7,back2
        SETB    SDA                   
        SETB    SCL                    
        END