1306.PDF

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DS1306
Serial Alarm Real Time Clock (RTC)
www.dalsemi.com
FEATURES
Real time clock counts seconds, minutes,
hours, date of the month, month, day of the
week, and year with leap year compensation
valid up to 2100
96-byte nonvolatile RAM for data storage
Two Time of Day Alarms - programmable on
combination of seconds, minutes, hours, and
day of the week
1 Hz and 32.768 kHz clock outputs
Serial interface supports Motorola Serial
Peripheral Interface (SPI) serial data ports or
standard 3-wire interface
Burst Mode for reading/writing successive
addresses in clock/RAM
Dual power supply pins for primary and
backup power supplies
Optional trickle charge output to backup
supply
2.0 - 5.5 volt operation
Optional industrial temperature range -40°C
to +85°C
Available in space-efficient 20-pin TSSOP
package
PIN ASSIGNMENT
V
CC2
V
BAT
X1
NC
X2
NC
INT0
INT1
1 Hz
GND
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
V
CC1
NC
32 KHz
V
CCIF
SDO
SDI
SCLK
NC
CE
SERMODE
DS1306 20-Pin TSSOP (173-mil)
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
V
CC1
32 KHz
V
CCIF
SDO
SDI
SCLK
CE
SERMODE
V
CC2
V
BAT
X1
X2
INT0
INT1
1 Hz
GND
DS1306 16-Pin DIP (300-mil)
PIN DESCRIPTION
ORDERING INFORMATION
DS1306
DS1306N
DS1306E
DS1306EN
16-Pin DIP
16-Pin DIP (Industrial)
20-Pin TSSOP
20-Pin TSSOP (Industrial)
V
CC1
V
CC2
V
BAT
V
CCIF
Input
GND
X1, X2
INT0
– Primary Power Supply
– Backup Power Supply
– +3 Volt Battery Input
– Interface Logic Power Supply
– Ground
– 32,768 Hz Crystal Connection
– Interrupt 0 Output
– Interrupt 1 Output
– Serial Data In
– Serial Data Out
– Chip Enable
– Serial Clock
– Serial Interface Mode
- 1 Hz Output
- 32.768 KHz Output
INT1
SDI
SDO
CE
SCLK
SERMODE
1 Hz
32 KHz
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DS1306
DESCRIPTION
The DS1306 Serial Alarm Real Time Clock provides a full BCD clock calendar which is accessed via a
simple serial interface. The clock/calendar provides seconds, minutes, hours, day, date, month, and year
information. The end of the month date is automatically adjusted for months with less than 31 days,
including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with
AM/PM indicator. In addition 96 bytes of nonvolatile RAM are provided for data storage.
An interface logic power supply input pin (V
CCIF
) allows the DS1306 to drive SDO and 32 KHz pins to a
level that is compatible with the interface logic. This allows an easy interface to 3-volt logic in mixed
supply systems. The DS1306 offers dual power supplies as well as a battery input pin. The dual power
supplies support a programmable trickle charge circuit which allows a rechargeable energy source (such
as a super cap or rechargeable battery) to be used for a backup supply. The V
BAT
pin allows the device to
be backed up by a non-rechargeable battery. The DS1306 is fully operational from 2.0 to 5.5 volts.
Two programmable time of day alarms are provided by the DS1306. Each alarm can generate an interrupt
on a programmable combination of seconds, minutes, hours, and day. “Don’t care” states can be inserted
into one or more fields if it is desired for them to be ignored for the alarm condition. A 1 Hz and a 32 kHz
clock output are also available.
The DS1306 supports a direct interface to Motorola SPI serial data ports or standard 3-wire interface. An
easy-to-use address and data format is implemented in which data transfers can occur 1 byte at a time or
in multiple-byte burst mode.
OPERATION
The block diagram in Figure 1 shows the main elements of the Serial Alarm RTC. The following
paragraphs describe the function of each pin.
DS1306 BLOCK DIAGRAM
Figure 1
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DS1306
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). However, it is
important to insure that the pull-up resistors used with the pins are never pulled up to a value which is
greater than V
CC
+ 0.3V. It is also required to insure that during backup operation mode, the voltage
(x)
present at
INT0
and 1 Hz does never exceed the voltage of the backup source. At all times the current on
each pin should not exceed 4.0 mA at V
CC
= 5V, or 1.5 mA at V
CC
= 2.5V.
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DS1306
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.
32 KHz (32.768 kHz Clock Output)
- The 32 kHz pin provides a 32.768 KHz output. This signal is
always present.
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 DS1306 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.
RTC AND RAM ADDRESS MAP
The address map for the RTC and RAM registers of the DS1306 is shown in Figure 2. Data is written to
the RTC by writing to address locations 80h to 9Fh and is written to the RAM by writing to address
locations A0h to FFh. RTC data is read by reading address locations 00h to 1Fh and RAM data is read by
reading address locations 20h to 7Fh.
ADDRESS MAP
Figure 2
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DS1306
CLOCK, CALENDAR, AND ALARM
The time and calendar information is obtained by reading the appropriate register bytes. The real time
clock registers are illustrated in Figure 3. The time, calendar, and alarm are set or initialized by writing
the appropriate register bytes. Note that some bits are set to 0. These bits will always read 0 regardless of
how they are written. Also note that registers 12h to 1Fh (read) and registers 92h to 9Fh are reserved.
These registers will always read 0 regardless of how they are written. The contents of the time, calendar,
and alarm registers are in the Binary-Coded Decimal (BCD) format.
RTC REGISTERS
Figure 3
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