Rainbow Electronics DS1337 - Manual (Page 6)

DS1337 I 2 C Serial Real-Time Clock
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BLOCK DIAGRAM
OPERATION
The Block Diagram shows the main elements of the DS1337. As shown, communications to and from the DS1337
occur serially over an I
2 C 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 when V
CC
is ³ 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. Figure 1 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 SYMBOL MIN TYP MAX UNITS
Nominal Frequency f
O
32.768 kHz
Series Resistance ESR 45 k W
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.
ALARM,
TRICKLE
CHARGE, AND
CONTROL
REGISTERS
SERIAL BUS
INTERFACE AND
ADDRESS
REGISTER
OSCILLATOR
AND
DIVIDER
CONTROL
LOGIC
X1
X2
SCL
SDA
1Hz
1Hz/4.096kHz/8.192kHz/32.768kHz
MUX/
BUFFER
SQW/ INTB
USER BUFFER
(7 BYTES)
CLOCK AND
CALENDAR
REGISTERS
"C" VERSION
ONLY
INTA
Dallas
Semiconductor
DS1337