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HOW TO INTERFACE RTC DS1307 WITH PIC MICROCONTROLLER.

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**broken link removed**

connection of I2C is standardized among IC that support this function.
The difference in coding is only the address length. Usually RTC use only 1 byte address, while EEPROM requires 2 bytes
 
It is a very standard interface, but it can be tricky. Here is a section of a working program.

Hope it helps
kent

Code: 
	#define I2C_M_SPEED_100K                                 ;
;***********************************************;
; Baud Rate Genarator Reload value              ;
;***********************************************;    
	;I2C_M_SPEED_100K 
_QUOTIENT    EQU    CLOCK_FREQ / (4 * .100000)-1
_REMAINDER   EQU    CLOCK_FREQ % (4 * .100000)  ;
        #if     _REMAINDER != 0                 ;
_I2C_M_BAUD_COUNT    EQU     _QUOTIENT + 1      ; _I2C_MBAUDCOUNT is nearest to ((fosc/4)/I2C_MSPEED)-1,
        #else   ;_REMAINDER = 0                 ; which has to be written in SSPADD.
_I2C_M_BAUD_COUNT    EQU    _QUOTIENT           ; _I2C_MBAUDCOUNT = ((fosc/4)/I2C_MSPEED)-1, which has to be written in SSPADD.
        #endif                                 	; which has to be written in SSPADD.
;-----------------------------------------------;
        #if     _I2C_M_BAUD_COUNT > 255         ;
        ERROR "At this System frequency, the given I2C frequency is not attainable."
        #endif                                  ;
        #if     _I2C_M_BAUD_COUNT < 2           ;
        ERROR "At this System frequency, the given I2C frequency is not attainable."
        #endif                                  ;





;******************************************************************************	
I2C_INIT                                    ;
	movlw   0x028							; Enable MSSP module and Master mode
	movwf   SSPCON1                         ;
	movlw   _I2C_M_BAUD_COUNT				;
	movwf   SSPADD                          ; Loading SSPADD with baudrate generator
	RETURN                                 	;

I2C_SEND                                    ;
	CALL    I2C_WAIT                        ;
	BSF     SSPCON2,SEN                     ; Send START bit
	CALL    I2C_WAIT                       	; Wait till bus becomes Idle
	MOVLW   0x0D0							; SlaveAddress(with write bit)
	CALL    I2C_PUT                      	; Send to buf
	TSTFSZ	WREG
	NOP			;GOTO	I2C_SEND_ERROR					; Error, restart	
	CALL    I2C_ACK_RECV            		; Check whether Ack received
	CALL    I2C_WAIT                      	; Wait till bus becomes Idle

	MOVLW   0x000							; Location Address_HI
	CALL    I2C_PUT                      	;
	TSTFSZ	WREG
	NOP			;GOTO	I2C_SEND_ERROR					; Error, restart
	CALL    I2C_ACK_RECV            		; Check whether Ack received
	CALL    I2C_WAIT                       	; Wait till bus becomes Idle

	BCF		SEC,7							; Enable RTC
	BSF		HOUR,6
	MOVF	SEC,W							; Load W
	CALL	I2C_SEND_DATA_BYTE				; Send The Byte
	MOVF	MIN,W							; Load W 
	CALL	I2C_SEND_DATA_BYTE				; Send The Byte
	MOVF	HOUR,W							; Load W 
	CALL	I2C_SEND_DATA_BYTE				; Send The Byte
	MOVF	DAY,W							; Load W
	CALL	I2C_SEND_DATA_BYTE				; Send The Byte
	MOVF	DATE,W							; Load W
	CALL	I2C_SEND_DATA_BYTE				; Send The Byte
	MOVF	MONTH,W							; Load W
	CALL	I2C_SEND_DATA_BYTE				; Send The Byte
	MOVF	YEAR,W							; Load W
	CALL	I2C_SEND_DATA_BYTE				; Send The Byte
	MOVF	I2C_CNTRL,W						; Load W
	CALL	I2C_SEND_DATA_BYTE				; Send The Byte
	BSF     SSPCON2,PEN                     ; Send STOP bit
	BSF		INTCON,GIE
	RETURN
I2C_SEND_DATA_BYTE
	CALL    I2C_PUT                      	;
	TSTFSZ	WREG
	NOP			;GOTO	I2C_SEND_ERROR					; Error, restart
	CALL    I2C_ACK_RECV            		; Check whether Ack received
	CALL    I2C_WAIT						; Wait till bus becomes Idle
	RETURN
	
I2C_SEND_ERROR
	MOVLW	0x000							; Line 1 LOW
	MOVWF	LCD_CUR_ADDR_L					; SET Line 1 LOW
	MOVLW	0x000							; Line 1 HIGH
	MOVWF	LCD_CUR_ADDR_H					; Set Line 1 HIGH
	MOVLW  	0x04C
	MOVWF	LCD_CUR_DIR
	CALL	LCD_SET_ADDR					; Move cursor to 
	MOVLW	0x042
	CALL 	SEND_LCD_CMD					; Send MWRITE Command
	MOVLW	HIGH (MSG_60)           		; "ERROR"
	MOVWF	TABLE_INDEX_HI
    MOVLW	LOW (MSG_60)
    MOVWF	TABLE_INDEX_LO
	CALL	PUT_MSG							; Put on display
	GOTO	I2C_SEND
	
	
I2C_RECEIVE                                	;
	BCF		INTCON,GIE
	BSF     SSPCON2,SEN                     ; Send START bit
	CALL    I2C_WAIT                       	; Wait till bus becomes Idle
	MOVLW   0x0D0							; SlaveAddress(with write bit)
	CALL    I2C_PUT                      	;
	TSTFSZ	WREG
	NOP			;GOTO	I2C_RX_ERROR					; Error, restart
	CALL    I2C_ACK_RECV            		; Check whether Ack received
	CALL    I2C_WAIT                     	; Wait till bus becomes Idle

	MOVLW   0x000                           ; Send LocationAddress_Hi
	CALL    I2C_PUT                      	;
	TSTFSZ	WREG
	NOP			;GOTO	I2C_RX_ERROR					; Error, restart
	CALL    I2C_ACK_RECV            		; Check whether Ack received
	CALL    I2C_WAIT                       	; Wait till bus becomes Idle

	BSF     SSPCON2,RSEN                    ; Send RepeatedSTART bit
	CALL    I2C_WAIT                      	; Wait till bus becomes Idle
	movlw   0x0D1							; Send SlaveAddress(with read bit)
	CALL    I2C_PUT                      	;
	TSTFSZ	WREG
	NOP			;GOTO	I2C_RX_ERROR					; Error, restart
	CALL    I2C_ACK_RECV            		; Check whether Ack received
	CALL    I2C_WAIT                       	; Wait till bus becomes Idle

	CALL	I2C_RX_DATA_BYTE				; RECV The Byte
	MOVWF	SEC								; Load SEC
	CALL    SEND_I2C_ACK                    ; Send Ack
	CALL	I2C_RX_DATA_BYTE				; RECV The Byte
	MOVWF	MIN								; Load MIN
	CALL    SEND_I2C_ACK                    ; Send Ack
	CALL	I2C_RX_DATA_BYTE				; RECV The Byte
	MOVWF	HOUR							; Load HOUR
	CALL    SEND_I2C_ACK                    ; Send Ack
	CALL	I2C_RX_DATA_BYTE				; RECV The Byte
	MOVWF	DAY								; Load DAY
	CALL    SEND_I2C_ACK                    ; Send Ack
	CALL	I2C_RX_DATA_BYTE				; RECV The Byte
	MOVWF	DATE							; Load DATE
	CALL    SEND_I2C_ACK                    ; Send Ack
	CALL	I2C_RX_DATA_BYTE				; RECV The Byte
	MOVWF	MONTH							; Load MONTH
	CALL    SEND_I2C_ACK                    ; Send Ack
	CALL	I2C_RX_DATA_BYTE				; RECV The Byte
	MOVWF	YEAR							; Load YEAR
	CALL    SEND_I2C_ACK                    ; Send Ack
	CALL	I2C_RX_DATA_BYTE				; RECV The Byte
	MOVWF	I2C_CNTRL						; Load I2C_CNTRL
	CALL    SEND_I2C_NOACK                  ; Send NoAck if all 16 bytes received
	BSF     SSPCON2,PEN                     ; Send STOP bit
	CALL    I2C_WAIT						; Wait till bus becomes Idle
	BSF		INTCON,GIE
	RETURN
I2C_RX_DATA_BYTE
	BSF     SSPCON2,RCEN                    ; Enable the receiver, Cleared by hardw
	CALL    I2C_WAIT_TILL_RDY          		; Wait till Data is ready
	MOVF    SSPBUF,W                      	; Read received value in W
	RETURN

I2C_RX_ERROR
	MOVLW	0x000							; Line 1 LOW
	MOVWF	LCD_CUR_ADDR_L					; SET Line 1 LOW
	MOVLW	0x001							; Line 1 HIGH
	MOVWF	LCD_CUR_ADDR_H					; Set Line 1 HIGH
	MOVLW  	0x04C
	MOVWF	LCD_CUR_DIR
	CALL	LCD_SET_ADDR					; Move cursor to 
	MOVLW	0x042
	CALL 	SEND_LCD_CMD					; Send MWRITE Command
	MOVLW	HIGH (MSG_60)           		; "ERROR"
	MOVWF	TABLE_INDEX_HI
    MOVLW	LOW (MSG_60)
    MOVWF	TABLE_INDEX_LO
	CALL	PUT_MSG							; Put on display
	GOTO	I2C_RECEIVE

I2C_WAIT_TILL_RDY                         	; Wait till Data is Ready
	BTFSS   SSPSTAT,BF                      ; Checks transmission/reception in progress
	GOTO	I2C_WAIT_TILL_RDY          		;
	RETURN                                  ;

I2C_PUT                                     ;
	MOVWF   SSPBUF                          ; Load Buffer
	BTFSS   SSPCON1,WCOL                    ; Check for collision
	RETLW   0x000							; No Collision, Return
	BCF     SSPCON1,WCOL                    ; Collision, retrn with restart code
	RETLW   0x001							; Indicates Write Collision Error

SEND_I2C_ACK                                ;
	BCF     SSPCON2,ACKDT                   ;
	BSF     SSPCON2,ACKEN                   ; Acknowledge
	CALL    I2C_WAIT                        ; Wait till bus becomes Idle
	RETURN

SEND_I2C_NOACK                             	;
	BSF     SSPCON2,ACKDT                   ;
	BSF     SSPCON2,ACKEN                   ; NoAcknowledge
	CALL    I2C_WAIT						; Wait till bus becomes Idle
	RETURN
	                                        ;
I2C_ACK_RECV                           
	BTFSC	SSPCON2,ACKSTAT                 ;
	GOTO	I2C_NoAckErr                    ; Indicates No Acknowledge received
	RETURN

I2C_NoAckErr								; Slave Error, No Ack
	BSF     SSPCON2,PEN						; Free the Bus if NoAck is received from Slave
	MOVLW	0x000							; Line 1 LOW
	MOVWF	LCD_CUR_ADDR_L					; SET Line 1 LOW
	MOVLW	0x000							; Line 1 HIGH
	MOVWF	LCD_CUR_ADDR_H					; Set Line 1 HIGH
	MOVLW  	0x04C
	MOVWF	LCD_CUR_DIR
	CALL	LCD_SET_ADDR					; Move cursor to 
	MOVLW	0x042
	CALL 	SEND_LCD_CMD					; Send MWRITE Command
	MOVLW	HIGH (MSG_60)           		; "ERROR"
	MOVWF	TABLE_INDEX_HI
    MOVLW	LOW (MSG_60)
    MOVWF	TABLE_INDEX_LO
	CALL	PUT_MSG							; Put on display
	GOTO	MAIN_SCREEN

I2C_WAIT                                    ; Wait till I2C_ Bus is Idle
	CALL	I2C_IS_IDLE                   	;
	TSTFSZ	WREG                            ;
	GOTO	I2C_WAIT						; Not Ready, Loop again
	RETURN                                  ;

I2C_IS_IDLE
	movf    SSPCON2,W                       ;
	andlw   01fh                            ; Checks SEN,PEN,RSEN,RCEN,ACKEN
	btfss   STATUS,Z                        ;
	retlw   0x005							; Indicates Bus is not Idle
	btfsc   SSPSTAT,2						; Checks transmission in progress
	retlw   0x005							; Indicates Bus is not Idle
	retlw   0x000							; Indicates Bus is Idle

;******************************************************************************
 
Almost forgot.
Code: 
CBLOCK	0x000
		YEAR
		MONTH
		DATE
		DAY
		HOUR
		MIN
		SEC
		I2C_CNTRL
		ENDC

Look on you data sheet for the ports, and other setup for I2C.
Also, read up on interfacing to EEPROM, it is almost the same.
 
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