I made a mistake and had made an assumption. Your chip does not communicate via I2C. The one I'm using is. The following probably won't help you at all. Sorry.
Maybe this will be of some help. I recently got a DS1307 sample from Dallas Semiconductor. It has 56 bytes of memory. Once I was able to read and write the clock, I learned how to write and read back from its internal memory. Look at the attached code. I made a few changes to read and write to memory. In particular, look at the routines putMemDs1307 and getMemDs1307.
Does this help?
/*
* RTC Control v.01
* by <http://www.combustory.com> John Vaughters
* Credit to:
* Maurice Ribble - http://www.glacialwanderer.com/hobbyrobotics for RTC DS1307 code
*
* With this code you can set the date/time, retreive the date/time and use the extra memory of an RTC DS1307 chip.
* The program also sets all the extra memory space to 0xff.
* Serial Communication method with the Arduino that utilizes a leading CHAR for each command described below.
*
* Commands:
* T(00-59)(00-59)(00-23)(1-7)(01-31)(01-12)(00-99) - T(sec)(min)(hour)(dayOfWeek)(dayOfMonth)(month)(year) - T Sets the date of the RTC DS1307 Chip.
* Example to set the time for 02-Feb-09 @ 19:57:11 for the 3 day of the week, use this command - T1157193020209
* Q(1-2) - (Q1) Memory initialization (Q2) RTC - Memory Dump
*
* If command = "C" RTC1307 Get Time and Date
* If command = "P" RTC1307 Get Time and Date and put in memory
* If command = "G" RTC1307 Get Time and Date from memory and display
* Analog pin 4 - SDA (pin 5 on DS1307)
* Analog pin 5 - SCL (pin 6 on DS1307)
*/
#include <Wire.h>
int clockAddress = 0x68; // This is the I2C address
int command = 0; // This is the command char, in ascii form, sent from the serial port
long previousMillis = 0; // will store last time Temp was updated
byte second, minute, hour, dayOfWeek, dayOfMonth, month, year;
byte test;
byte trial;
// Convert normal decimal numbers to binary coded decimal
byte decToBcd(byte val)
{
return ( (val/10*16) + (val%10) );
}
// Convert binary coded decimal to normal decimal numbers
byte bcdToDec(byte val)
{
return ( (val/16*10) + (val%16) );
}
// 1) Sets the date and time on the ds1307
// 2) Starts the clock
// 3) Sets hour mode to 24 hour clock
// Assumes you're passing in valid numbers,
// Probably need to put in checks for valid numbers.
void setDateDs1307()
{
// Use of (byte) type casting and ascii math to achieve result.
second = (byte) ((Serial.read() - 48) * 10 + (Serial.read() - 48));
minute = (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
hour = (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
dayOfWeek = (byte) (Serial.read() - 48);
dayOfMonth = (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
month = (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
year= (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
Wire.beginTransmission(clockAddress);
Wire.send(0x00);
Wire.send(decToBcd(second)); // 0 to bit 7 starts the clock
Wire.send(decToBcd(minute));
Wire.send(decToBcd(hour)); // If you want 12 hour am/pm you need to set
// bit 6 (also need to change readDateDs1307)
Wire.send(decToBcd(dayOfWeek));
Wire.send(decToBcd(dayOfMonth));
Wire.send(decToBcd(month));
Wire.send(decToBcd(year));
Wire.endTransmission();
}
// Gets the date and time from the ds1307 and prints result
void getDateDs1307() { // Reset the register pointer
Wire.beginTransmission(clockAddress);
Wire.send(0x00);
Wire.endTransmission();
Wire.requestFrom(clockAddress, 7);
// A few of these need masks because certain bits are control bits
second = bcdToDec(Wire.receive() & 0x7f);
minute = bcdToDec(Wire.receive());
// Need to change this if 12 hour am/pm
hour = bcdToDec(Wire.receive() & 0x3f);
dayOfWeek = bcdToDec(Wire.receive());
dayOfMonth = bcdToDec(Wire.receive());
month = bcdToDec(Wire.receive());
year = bcdToDec(Wire.receive());
Serial.print(hour, DEC);
Serial.print(":");
Serial.print(minute, DEC);
Serial.print(":");
Serial.print(second, DEC);
Serial.print(" ");
Serial.print(month, DEC);
Serial.print("/");
Serial.print(dayOfMonth, DEC);
Serial.print("/");
Serial.print(year, DEC);
}
void getTimeDs1307() {
Wire.beginTransmission(clockAddress);
Wire.send(0x00); // Reset the register pointer
Wire.endTransmission();
Wire.requestFrom(clockAddress, 7);
second = (Wire.receive() & 0x7f);
minute = (Wire.receive());
hour = (Wire.receive() & 0x3f);
dayOfWeek = (Wire.receive());
dayOfMonth = (Wire.receive());
month = (Wire.receive());
year = (Wire.receive());
}
void putMemDs1307() {
//get the time from the clock and then put into memory address 0x08
//this routine can be used for data logging purposes
Wire.beginTransmission(clockAddress);
Wire.send(0x08);
Wire.send(second);
Wire.send(minute);
Wire.send(hour);
Wire.send(dayOfWeek);
Wire.send(dayOfMonth);
Wire.send(month);
Wire.send(year);
Wire.endTransmission();
/* The following is commented out. It was originally used to see what was being put into memory
and then compared to what I pulled from memory. One I was comfortable with the results,
I no longer used this code.
Serial.print(hour, DEC);
Serial.print(":");
Serial.print(minute, DEC);
Serial.print(":");
Serial.print(second, DEC);
Serial.print(" ");
Serial.print(month, DEC);
Serial.print("/");
Serial.print(dayOfMonth, DEC);
Serial.print("/");
Serial.print(year, DEC);
*/
}
void getMemDs1307() {
// Get the contents of memory location 0x08 and send to the PC for display
Wire.beginTransmission(clockAddress);
Wire.send(0x08);
Wire.endTransmission();
Wire.requestFrom(clockAddress, 7); //request 7 bytes from the clock
// A few of these need masks because certain bits are control bits
second = bcdToDec(Wire.receive() & 0x7f); //byte #1
minute = bcdToDec(Wire.receive()); //byte #2
hour = bcdToDec(Wire.receive() & 0x3f); //byte #3...
dayOfWeek = bcdToDec(Wire.receive());
dayOfMonth = bcdToDec(Wire.receive());
month = bcdToDec(Wire.receive());
year = bcdToDec(Wire.receive());
Serial.print(hour, DEC); //print the values to the PC
Serial.print(":");
Serial.print(minute, DEC);
Serial.print(":");
Serial.print(second, DEC);
Serial.print(" ");
Serial.print(month, DEC);
Serial.print("/");
Serial.print(dayOfMonth, DEC);
Serial.print("/");
Serial.print(year, DEC);
}
void setup() {
Wire.begin();
Serial.begin(57600);
}
void loop() {
if (Serial.available()) { // Look for char in serial que and process if found
command = Serial.read();
if (command == 84) { //If command = "T" Set Date
setDateDs1307();
getDateDs1307();
Serial.println(" ");
}
else if(command == 67){ //If command = "C" RTC1307 Get Time and Date
getDateDs1307();
Serial.println(" ");
}
else if(command == 80){ //If command = "P" RTC1307 Get Time and Date and put in memory
getTimeDs1307();
putMemDs1307();
Serial.println(" ");
}
else if(command == 71){ //If command = "G" RTC1307 Get Time and Date from memory and display
getMemDs1307();
Serial.println(" ");
}
else if (command == 81) { //If command = "Q" RTC1307 Memory Functions
delay(100);
if (Serial.available()) {
command = Serial.read();
// If command = "1" RTC1307 Initialize Memory - All Data will be set to 255 (0xff).
// Therefore 255 or 0 will be an invalid value.
if (command == 49) {
// 255 will be the init value and 0 will be cosidered an error that
// occurs when the RTC is in Battery mode.
Wire.beginTransmission(clockAddress);
// Set the register pointer to be just past the date/time registers.
Wire.send(0x08);
for (int i = 1; i <= 27; i++) {
Wire.send(0xff);
delay(100);
}
Wire.endTransmission();
getDateDs1307();
Serial.println(": RTC1307 Initialized Memory");
}
else if (command == 50) { //If command = "2" RTC1307 Memory Dump
getDateDs1307();
Serial.println(": RTC 1307 Dump Begin");
Wire.beginTransmission(clockAddress);
Wire.send(0x00);
Wire.endTransmission();
Wire.requestFrom(clockAddress, 64);
for (int i = 1; i <= 64; i++) {
test = Wire.receive();
Serial.print(i);
Serial.print(":");
Serial.println(test, DEC);
}
Serial.println(" RTC1307 Dump end");
}
}
}
Serial.print("Command: ");
Serial.println(command); // Echo command CHAR in ascii that was sent
}
command = 0; // reset command
delay(100);
}