
DS1305
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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 DS1305 that can be used as an
interrupt input to a processor.  The 
INT0
  pin can be programmed to be asserted by only Alarm 0 or can be
programmed to be asserted by either Alarm 0 or Alarm 1.  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 DS1305 is powered by V
CC1
, V
CC2
, or V
BAT
.  The 
INT0
  pin is an open drain output and
requires an external pull-up resistor.
INT1
(Interrupt 1 Output)
- The 
INT1
 pin is an active low output of the DS1305 that can be used as an
interrupt input to a processor.  The 
INT1
 pin can be programmed to be asserted by Alarm 1 only.  The
INT1
 pin remains low as long as the status bit causing the interrupt is present and the corresponding
interrupt enable bit is set.  The 
INT1
 pin operates when the DS1305 is powered by V
CC1
, V
CC2
, or V
BAT
.
The 
INT1
 pin is an open drain output and requires an external pull-up resistor.
Both 
INT0
 and 
INT1
are open drain outputs.  The two interrupts and the internal clock continue to run
regardless of the level of V
CC
(as long as a power source is present).
PF
(Power Fail Output)
- The 
PF
 pin is used to indicate loss of the primary power supply (V
CC1
).
When V
CC1
is less than V
CC2
or is less than V
BAT
, the 
PF
 pin will be driven low.
X1, X2
- Connections for a standard 32.768 kHz quartz crystal.  The internal oscillator is designed for
operation with a crystal having a specified load capacitance of 6 pF.  For more information on crystal
selection and crystal layout considerations, please consult Application Note 58, “Crystal Considerations
with Dallas Real Time Clocks.” The DS1305 can also be driven by an external 32.768 kHz oscillator.  In
this configuration, the X1 pin is connected to the external oscillator signal and the X2 pin is floated.