
DS1306
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SIGNAL DESCRIPTIONS
V
CC1
- DC power is provided to the device on this pin.  V
CC1
 is the primary power supply.
V
CC2
- This is the secondary power supply pin.  In systems using the trickle charger, the rechargeable
energy source is connected to this pin.
V
BAT
- Battery input for any standard 3-volt lithium cell or other energy source.
V
CCIF
 (Interface Logic Power Supply Input) - 
The V
CCIF
 pin allows the DS1306 to drive SDO and
32 kHz output pins to a level that is compatible with the interface logic, thus allowing an easy interface to
3-volt logic in mixed supply systems.  This pin is physically connected to the source connection of the p-
channel transistors in the output buffers of the SDO and 32 kHz pins.
SERMODE (Serial Interface Mode Input) - 
The SERMODE pin offers the flexibility to choose
between two serial interface modes.  When connected to GND, standard 3-wire communication is
selected.  When connected to V
CC
, Motorola SPI communication is selected.
SCLK (Serial Clock Input) 
- SCLK is used to synchronize data movement on the serial interface for
either the SPI or 3-wire interface.
SDI (Serial Data Input) - 
When SPI communication is selected, the SDI pin is the serial data input for
the SPI bus.  When 3-wire communication is selected, this pin must be tied to the SDO pin (the SDI and
SDO pins function as a single I/O pin when tied together).
SDO (Serial Data Output)
- 
When SPI communication is selected, the SDO pin is the serial data output
for the SPI bus.  When 3-wire communication is selected, this pin must be tied to the SDI pin (the SDI
and SDO pins function as a single I/O pin when tied together).
CE (Chip Enable) 
- The Chip Enable signal must be asserted high during a read or a write for both
3-wire and SPI communication.  This pin has an internal 55k pull-down resistor (typical).
INT0
  (Interrupt 0 Output) 
- The 
INT0
 pin is an active low output of the DS1306 that can be used as an
interrupt input to a processor.  The 
INT0
 pin can be programmed to be asserted by Alarm 0.  The 
INT0
pin remains low as long as the status bit causing the interrupt is present and the corresponding interrupt
enable bit is set.  The 
INT0
 pin operates when the DS1306 is powered by V
CC1
, V
CC2
, or V
BAT
.  The 
INT0
pin is an open drain output and requires an external pullup resistor.
1 Hz (1 Hz Clock Output) 
- The 1 Hz pin provides a 1 Hz squarewave output.  This output is active
when the 1 Hz bit in the control register is a logic 1.
Both 
INT0
 and 1 Hz pins are open drain outputs.  The interrupt, 1 Hz signal, and the internal clock
continue to run regardless of the level of V
CC
 (as long as a power source is present).
INT1 (Interrupt 1 Output) 
- The INT1 pin is an active high output of the DS1306 that can be used as an
interrupt input to a processor.  The INT1 pin can be programmed to be asserted by alarm 1.  When an
alarm condition is present, the INT1 pin generates a 62.5 ms active high pulse.  The INT1 pin operates
only when the DS1306 is powered by V
CC2
 or V
BAT
.  When active, the INT1 pin is internally pulled up to
V
CC2
 or V
BAT
.  When inactive, the INT1 pin is internally pulled low.