You need a voltage translator to interface the DUE’s 3.3V logic to the DS1307’s 5V logic.
Something like this should work (but there are also many, many others):
See fig 10 of the P82B96 datasheet. The +5V pullup you see on the left of this figure is already taken care of on the DUE board (it is actually pulled up to 3.3V on the DUE pcb).
Apply 5V (Vcc) to the P82B96 (“pin 8”), and add your own pullup resistors to 5V for SDA and SCL that go to the DS1307’s I2C interface (10k are usually fine).
This figure shows one-half of the connections. You would need to connect the SCL line in a similar manner.
The DS1307 maxes out at a 100KHz I2C clock. The DUE’s default I2C clock rate is 100KHz.
Some warnings about I2C on the DUE:
- The DUE board has crazy-low-value pullup resistors on the TWI (I2C) lines. Be aware of this. Any more current load on these pins (from additional pullups) can destroy your board. See the wonderful pin-out diagram at the top of this forum for pin capabilities.
- The I2C library in 1.5.2 is still very limited. Search the forum for issues. It looks to me that this gadget should work fine, as long as you avoid the protocol shown on “Figure 6. Data Read (Write Pointer, Then Read)—Slave Receive and Transmit” in the DS1307 datasheet.
I can’t believe I mentioning this, but:
The DS1307 may work if you attach the I2C lines (SDA and SCL) to the DUE directly (without using the translator chip). Be absolutely certain that there are not any existing pullup resistors on the DS1307 I2C lines. If there are existing resistors, then you need to remove them completely from the DS1307 board, as these resistors are probably connected to +5V (which is undesirable/dangerous for the DUE). I am not familiar with the adafriut DS1307 board, you will need to figure this out yourself. http://www.adafruit.com/products/264?
Not using a proper voltage translator chip may result in inconsistent operation of the DS1307, but no damage should be done to either the DUE or the DS1307 (as long as the warnings shown above are understood and followed).
If you don’t understand these issues, then please Google some more, and then ask more questions here…