C18 code for interfacing a PIC to a DS 12885 / DS 12887 2011-02-26

//Cut and paste these register definitions in your main code, 
//add this C file and call the read and write functions
//whenever a Read or Write operation is to be performed.The syntax of the functions is:
//write_RTC(address,data);
//data=read_RTC(address);
// where data and address are 8 bit unsigned characters.
//This snippet has been tested using an 18F4620 and uses PORTD as the Data Bus,
//RE0 for Address strobe,RE1 for RW and RE2 for Data strobe. You can change this by
//changing the Pin Definitions


/****************************Register Definitions**************************************/
#define sec 0
#define sec_alarm 1
#define min 2
#define min_alarm 3
#define hours 4
#define hour_alarm 5
#define day_week 6
#define day_month 7
#define month 8
#define year 9
#define REGA 10
#define REGB 11
#define REGC 12
#define REGD 13 
void write_RTC(unsigned char, unsigned char );
unsigned char read_RTC(unsigned char);	
/*************************************************************************************/
	
/*******************Pin Definitions of the RTC****************************************/
#define ADwritebus LATD           			//Write Bus for the RTC
#define AS LATEbits.LATE0         			//Address Strobe line for the RTC
#define DS LATEbits.LATE2         			//Data Strobe line for the RTC 
#define RW_bar LATEbits.LATE1     			//Read/Write signal for the RTC
#define ADreadbus PORTD           			//Read Bus for the RTC
#define DBus_Direction TRISD      			//Bus direction setter for Data Bus
#define AS_Direction TRISEbits.TRISE0           //Bus direction setter for Data Bus
#define DS_Direction TRISEbits.TRISE2      			//Bus direction setter for Data Bus
#define RW_bar_Direction TRISEbits.TRISE1     	//Bus direction setter for Data Bus
/*************************************************************************************/


void write_RTC(unsigned char RTCwaddress, unsigned char RTCwdata)
{	
	AS_Direction=0;		 //Make all control signal pins as outputs
	DS_Direction=0;
	RW_bar_Direction=0;
	DBus_Direction=0;        //Make data bus an output bus since this is a write operation
	DS=1;
	RW_bar=1;
	AS=1;
	ADwritebus=RTCwaddress;
	_asm nop _endasm
	AS=0;  //Latch address		
	_asm nop _endasm
	ADwritebus=0;		//Make address/data line zero		
	RW_bar=0;               
	_asm nop _endasm
	ADwritebus=RTCwdata;	//write data on specific address	
	_asm nop _endasm
	RW_bar=1;	            //Enable writing the data.
	_asm NOP _endasm
	ADwritebus=0;
	AS=1;
}
unsigned char read_RTC(unsigned char RTCraddress)
{	
	
	unsigned char *pd;
	AS_Direction=0;		 //Make all control signal pins as outputs
	DS_Direction=0;
	RW_bar_Direction=0;
	DBus_Direction=0;       //Make data bus an output bus for address writing
	DS=1;
	RW_bar=1;
	AS=1;
	ADwritebus=RTCraddress;
	_asm nop _endasm
	AS=0;
	DBus_Direction=0xff;   //Make data bus an input bus for data reading
	_asm nop _endasm
	DS=0;
	_asm nop _endasm
	*pd=ADreadbus;
	DS=1;
	_asm NOP _endasm
	AS=1;
	_asm NOP _endasm

	return(*pd);
}