DP8572AN National Semiconductor, DP8572AN Datasheet - Page 13

• Manufacturer Part Number: DP8572AN
• Description: IC REAL TIME CLOCK W/RAM 24 DIP
• Manufacturer: National Semiconductor
• Type: Clock/Calendar/NVSRAMr

Specifications of DP8572AN

• Memory Size: 44B
• Time Format: HH:MM:SS:hh (12/24 hr)
• Date Format: YY-MM-DD-dd
• Interface: Parallel
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 24-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *DP8572AN; DP8572

Functional Description
If chip select is low when a power failure is detected a
safety circuit will ensure that if a read or write is held active
continuously for greater than 30 s after the power fail sig-
nal is asserted the lock-out will be forced If a lock-out delay
is enabled the DP8572A will remain active for 480 s after
power fail is detected This will enable the
last minute bookkeeping before total system collapse
When the host CPU is finished accessing the RTC it may
force the bus lock-out before 480 s has elapsed by reset-
ting the delay enable bit
The battery switch over circuitry is completely independent
of the PFAIL pin A separate circuit compares V
V
to operate from the V
voltage At this time the battery supply is switched in V
disconnected and the device is now in the standby mode If
indeterminate operation of the battery switch over circuit is
to be avoided then the voltage at the V
allowed to equal the voltage at the V
After the generation of a lock-out signal and eventual
switch in of the battery supply the pins of the RTC will be
configured as shown in Table II Outputs that have a pull-up
BB
voltage As the main supply fails the RTC will continue
CC
pin until V
FIGURE 6 System-Battery Switchover (Upper Left) Power Fail
CC
BB
(Continued)
falls below the V
CC
pin
pin must not be
and Lock-Out Circuits (Lower Right)
P to perform
CC
to the
CC
BB
is
13
resistor should be connected to a voltage no greater than
V
The Interrupt Power Fail Operation bit in the Real-Time
Mode Register determine whether or not the interrupts will
continue to function after a power fail event
As power returns to the system the battery switch over cir-
cuit will switch back to V
greater than the battery voltage The chip will remain in the
locked out state as long as PFAIL
BB
CS RD WR
INTR MFO
Oscillator
TABLE II Pin Isolation during a Power Failure
D0– D7
A0– A4
PFAIL
Pin
Locked Out
Locked Out
Locked Out
Not Isolated
Not Isolated
Not Isolated
PFAIL
Logic 0
CC
power as soon as it becomes
e
e
0 When PFAIL
Standby Mode
Locked Out
Locked Out
Locked Out
Not Isolated
Not Isolated
Open Drain
V
BB l
TL F 9980 – 11
V
CC
e
1