and 512 Bytes EEPROM

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9

Detailed Description

multifunction device that provides a clock/calendar,

programmable watchdog timer, power-supply monitor

with reset, and 512 bytes of EEPROM. The clock pro-

vides hundredths of seconds, seconds, minutes, and

hours, and operates in 24-hour or 12-hour format with

an AM/PM indicator. The calendar provides day, date,

month, and year information. The date at the end of the

month is automatically adjusted for months with fewer

than 31 days, including corrections for leap year. A

watchdog timer provides a reset for an unresponsive

microprocessor. It is programmable in 10ms intervals

from 0.01 to 99.99 seconds. A temperature-compensat-

ed voltage reference and comparator circuit monitors

the device automatically switches to the backup supply

and drives the reset output to the active state. When

period to allow the power supply and processor to sta-

bilize. The device also has a pushbutton reset con-

troller, which debounces a reset input signal. The

Operation

Access is obtained by implementing a START condition

and providing a device identification code followed by

data. Subsequent registers can be accessed sequen-

tially until a STOP condition is executed. See the Block

Diagram, which shows the main elements of the serial

real-time clock.

Power Control

The power-control function is provided by a precise,

temperature-compensated voltage reference and a

device is fully accessible and data can be written and

after RST goes high (Figure 1).

Oscillator Circuit

The DS1388 uses an external 32.768kHz crystal. The

oscillator circuit does not require any external resistors

or capacitors to operate. Table 2 specifies several

crystal parameters for the external crystal, and Figure 3

shows a functional schematic of the oscillator circuit.

Using a crystal with the specified characteristics, the

startup time is usually less than one second.

SUPPLY CONDITION

READ/WRITE

ACCESS

POWERED

BY

No

No

Yes

Yes

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

Nominal

Frequency

32.768

kHz

Series

Resistance

ESR

50

k

Ω

Load

Capacitance

6pF

*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 addi-

tional specifications.

Table 1. Power Control

Table 2. Crystal Specifications*