DS1305
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 VCC1, VCC2, or VBAT. 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 VCC1, VCC2, or VBAT
.
The INT1 pin is an open drain output and requires an external pull-up resistor.
Both INT0 and INT1are open drain outputs. The two interrupts and the internal clock continue to run
regardless of the level of VCC (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 (VCC1).
When VCC1 is less than VCC2 or is less than VBAT , 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.
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DALLAS [ DALLAS SEMICONDUCTOR ]
