DS1337_06 Datasheet, PDF (6/15 Pages) Maxim Integrated Products – I2C Serial Real-Time Clock

BLOCK DIAGRAM
DS1337 I²C Serial Real-Time Clock
X1
X2
DS1338C ONLY
SCL
SDA
1Hz/4.096kHz/8.192kHz/32.768kHz
C_L
1Hz
C_L
OSCILLATOR
AND DIVIDER
Dallas
Semiconductor
DS1337
CONTROL
LOGIC
SERIAL BUS
INTERFACE AND
ADDRESS
REGISTER
MUX/ ^SQW/INTB
BUFFER
ALARM AND
CONTROL
REGISTERS
INTA
CLOCK AND
CALENDAR
REGISTERS
USER BUFFER
(7 BYTES)
DETAILED DESCRIPTION
The Block Diagram shows the main elements of the DS1337. As shown, communications to and from the DS1337
occur serially over an I²C bus. The DS1337 operates as a slave device on the serial bus. Access is obtained by
implementing a START condition and providing a device identification code, followed by data. Subsequent
registers can be accessed sequentially until a STOP condition is executed. The device is fully accessible through
the I²C interface whenever V_CC is between 5.5V and 1.8V. I²C operation is not guaranteed when V_CC is below 1.8V.
The DS1337 maintains the time and date when V_CC is as low as 1.3V.
OSCILLATOR CIRCUIT
The DS1337 uses an external 32.768kHz crystal. The oscillator circuit does not require any external resistors or
capacitors to operate. Table 1 specifies several crystal parameters for the external crystal. The Block Diagram
shows a functional schematic of the oscillator circuit. The startup time is usually less than 1 second when using a
crystal with the specified characteristics.
Table 1. Crystal Specifications*
PARAMETER
Nominal Frequency
Series Resistance
SYMBOL
f_O
ESR
MIN TYP MAX
32.768
50
UNITS
kHz
kΩ
Load Capacitance
C_L
6
pF
*The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to
Application Note 58: Crystal Considerations for Dallas Real-Time Clocks for additional specifications.
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