DS1388 Maxim, DS1388 Datasheet - Page 9

• Manufacturer Part Number: DS1388
• Description: The DS1388 I²C real-time clock (RTC), supervisor, and EEPROM is a multifunction device that provides a clock/calendar, programmable watchdog timer, power-supply monitor with reset, and 512 bytes of EEPROM
• Manufacturer: Maxim

The DS1388 I
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 status of V
the device automatically switches to the backup supply
and drives the reset output to the active state. When
V
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
device is accessed through an I
The DS1388 operates as a slave device on the I
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.
The power-control function is provided by a precise,
temperature-compensated voltage reference and a
comparator circuit that monitors the V
device is fully accessible and data can be written and
read when V
V
blocked from any access. If V
the device power is switched from V
when V
V
CC
CC
BACKUP
returns to nominal levels, the reset is held low for a
falls below V
CC
, the device power is switched from V
drops below V
CC
CC
2
C RTC, supervisor, and EEPROM is a
. If a primary power failure is detected,
is greater than V
I
PF
2
, the internal clock registers are
Detailed Description
C RTC/Supervisor with Trickle Charger
PF
PF
. If V
2
Power Control
C serial interface.
is less than V
PF
PF
. However, when
_____________________________________________________________________
Operation
CC
is greater than
CC
to V
level. The
BACKUP
BACKUP
2
C bus.
CC
to
,
and 512 Bytes EEPROM
V
ters are maintained from the V
is returned to nominal levels (Table 1). After V
returns above V
after RST goes high (Figure 1).
On first application of power to the device, the time and
date registers are set to 00/00/00 00 00:00:00
(MM/DD/YY DOW HH:MM:SS). The user should initial-
ize all RTC registers to valid date and time settings.
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. Using a
crystal with the specified characteristics, the startup
time is usually less than one second.
Table 1. Power Control
Table 2. Crystal Specifications*
* 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.
Nominal
Frequency
Series
Resistance
Load
Capacitance
BACKUP
V
PARAMETER
V
V
V
CC
CC
CC
CC
SUPPLY CONDITION
< V
< V
> V
> V
PF
PF
PF
PF
when V
, V
, V
, V
, V
CC
CC
CC
CC
< V
> V
< V
> V
PF
SYMBOL
CC
BACKPUP
, read and write access is allowed
ESR
BACKUP
BACKUP
BACKUP
C
f
O
drops below V
L
Oscillator Circuit
MIN
READ/WRITE
BACKUP
ACCESS
Yes
Yes
32.768
No
No
TYP
BACKUP
6
source until V
MAX
50
. The regis-
POWERED
V
BACKUP
V
V
V
BY
CC
CC
CC
UNITS
kHz
kΩ
pF
CC
CC
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