DS1305
PIN DESCRIPTION
PIN
FUNCTION
NAME
DIP
TSSOP
Backup Power Supply. This is the secondary power supply pin. In systems
1
1
VCC2
using the trickle charger, the rechargeable energy source is connected to this
pin.
Battery Input for Standard +3V Lithium Cell or Other Energy Source. If not
used, VBAT must be connect to ground. Diodes must not be placed in series
between VBAT and the battery, or improper operation will result. UL
recognized to ensure against reverse charging current when used in
conjunction with a lithium battery. See “Conditions of Acceptability” at
www.maxim-ic.com/TechSupport/QA/ntrl.htm.
2
3
2
VBAT
Connections for Standard 32.768kHz Quartz Crystal. The internal oscillator is
designed for operation with a crystal having a specified load capacitance of
6pF. For more information on crystal selection and crystal layout
considerations, refer to Application Note 58: Crystal Considerations with
Dallas Real-Time Clocks. The DS1305 can also be driven by an external
32.768kHz oscillator. In this configuration, the X1 pin is connected to the
external oscillator signal and the X2 pin is floated.
3
5
X1
4
5
X2
4, 6, 8,
13, 19
N.C.
No Connection
Active-Low 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
INT0
6
7
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
pullup resistor.
,
Active-Low 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
INT1
7
9
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 pullup resistor. Both INT0 and INT1 are 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).
8
9
10
11
GND
Ground
Serial Interface Mode. 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 VCC, SPI communication is
selected.
SERMODE
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
pulldown resistor (typical).
10
11
12
14
CE
Serial Clock Input. SCLK is used to synchronize data movement on the serial
interface for either the SPI or 3-wire interface.
SCLK
3 of 22
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