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PRELIMINARY
December 1993
LV8573A Low Voltage Real Time Clock (RTC)
General Description
The LV8573A is intended for use in microprocessor based
systems where information is required for multi-tasking data
logging or general time of day date information This device
is implemented in low voltage silicon gate microCMOS tech-
nology to provide low standby power in battery back-up en-
vironments The circuit’s architecture is such that it looks
like a contiguous block of memory or I O ports organized as
one block of 32 bytes This includes the Control Registers
the Clock Counters the Alarm Compare RAM and the Time
Save RAM
Time and date are maintained from 1 100 of a second to
year and leap year in a BCD format 12 or 24 hour modes
Day of week and day of month counters are provided Time
is controlled by an on-chip crystal oscillator requiring only
the addition of the 32 768 kHz crystal and two capacitors
Power failure logic and control functions have been integrat-
ed on chip This logic is used by the RTC to issue a power
fail interrupt and lock out the mP interface The time power
fails may be logged into RAM automatically when VBB l
VCC Additionally two supply pins are provided When VBB
l VCC internal circuitry will automatically switch from the
main supply to the battery supply
The LV8573A’s interrupt structure provides three basic
types of interrupts Periodic Alarm Compare and Power
Fail Interrupt mask and status registers enable the masking
and easy determination of each interrupt
Features
Y 3 3V g10% supply
Y Full function real time clock calendar
12 24 hour mode timekeeping
Day of week counter
Parallel resonant oscillator
Y Power fail features
Internal power supply switch to external battery
Power Supply Bus glitch protection
Automatic log of time into RAM at power failure
Y On-chip interrupt structure
Periodic alarm and power fail interrupts
Block Diagram
FIGURE 1
TRI-STATE is a registered trademark of National Semiconductor Corporation
C1995 National Semiconductor Corporation TL F 11418
TL F 11418 – 1
RRD-B30M105 Printed in U S A

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Absolute Maximum Ratings (Notes 1 2)
If Military Aerospace specified devices are required
please contact the National Semiconductor Sales
Office Distributors for availability and specifications
Supply Voltage (VCC)
DC Input Voltage (VIN)
DC Output Voltage (VOUT)
Storage Temperature Range
b0 5V to a7 0V
b0 5V to VCC a0 5V
b0 5V to VCC a 0 5V
b65 C to a150 C
Power Dissipation (PD)
500 mW
Lead Temperature (Soldering 10 sec )
260 C
Operation Conditions
Supply Voltage (VCC) (Note 3)
Supply Voltage (VBB) (Note 3)
DC Input or Output Voltage
(VIN VOUT)
Operation Temperature (TA)
Electr-Static Discharge Rating
Min
30
22
00
b40
Typical Values
iJA DIP
Board
Socket
iJA PLCC Board
Socket
Max
36
VCCb0 4
VCC
a85
1
61 C W
67 C W
80 C W
88 C W
Unit
V
V
V
C
kV
DC Electrical Characteristics
VCC e 3 3V g10% VBB e 2 5V VPFAIL l VIH CL e 100 pF unless otherwise specified
Symbol
Parameter
Conditions
Min Max
VIH High Level Input Voltage
(Note 4)
VIL Low Level Input Voltage
Any Inputs Except OSC IN
OSC IN with External Clock
All Inputs Except OSC IN
OSC IN with External Clock
20
VBB b 0 2
b0 3
b0 3
VCC a0 3
08
02
VOH
VOL
IIN
IOZ
ILKG
High Level Output Voltage
(Excluding OSC OUT INTR)
Low Level Output Voltage
(Excluding OSC OUT)
Input Current (Except OSC IN)
Output TRI-STATE Current
Output High Leakage Current
MFO INTR Pins
IOUT e b20 mA
IOUT e b2 0 mA
IOUT e b20 mA
IOUT e 2 0 mA
VIN e VCC or GND
VOUT e VCC or GND
VOUT e VCC or GND
Outputs Open Drain
VCC b0 2
24
02
03
g0 7
g1
g1
ICC Quiescent Supply Current
(Note 6)
ICC Quiescent Supply Current
(Single Supply Mode)
(Note 7)
IBB Standby Mode Battery
Supply Current
(Note 7)
IBLK Battery Leakage
FOSC e 32 768 kHz
VIN e VCC or GND (Note 5)
VIN e VCC or GND (Note 6)
VIN e VIH or VIL (Note 6)
VBB e GND
VIN e VCC or GND
FOSC e 32 768 kHz
VCC e GND
OSC OUT e open circuit
other pins e GND
FOSC e 32 768 kHz
2 2V s VBB s 2 6V
other pins at GND
VCC e GND VBB e 2 6V
VCC e 3 6V VBB e 2 2V
b0 8
220
700
5
30
8
08
Note 1 Absolute Maximum Ratings are those values beyond which damage to the device may occur
Note 2 Unless otherwise specified all voltages are referenced to ground
Note 3 In battery backed mode VBB s VCC b 0 4V
Single Supply Mode Data retention voltage is 2 2V min
In single Supply Mode (Power connected to VCC pin) 3 0V s VCC s 3 6V
Note 4 This parameter (VIH) is not tested on all pins at the same time
Note 5 This specification tests ICC with all power fail circuitry disabled by setting D7 of Interrupt Control Register 1 to 0
Note 6 This specification tests ICC with all power fail circuitry enabled by setting D7 of Interrupt Control Register 1 to 1
Note 7 OSC IN is driven by a signal generator Contents of the Test Register e 00(H) and the MFO pin is not configured as buffered oscillator out
Units
V
V
V
V
V
V
V
V
mA
mA
mA
mA
mA
mA
mA
mA
mA
mA
2

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AC Electrical Characteristics
VCC e 3 3V g10% VBB e 2 5V VPFAIL l VIH CL e 100 pF unless otherwise specified
Symbol
Parameter
Min Max Units
READ TIMING
tAR Address Valid Prior to Read Strobe
10
tRW Read Strobe Width (Note 8)
100
tCD Chip Select to Data Valid Time
100
tRAH
Address Hold after Read (Note 9)
2
tRD Read Strobe to Valid Data
90
tDZ Read or Chip Select to TRI-STATE
80
tRCH
Chip Select Hold after Read Strobe (Note 9)
0
tDS
Minimum Inactive Time between Read or Write Accesses
70
WRITE TIMING
ns
ns
ns
ns
ns
ns
ns
ns
tAW
tWAH
tCW
tWW
tDW
tWDH
tWCH
INTERRUPT TIMING
Address Valid before Write Strobe
Address Hold after Write Strobe (Note 9)
Chip Select to End of Write Strobe
Write Strobe Width (Note 10)
Data Valid to End of Write Strobe
Data Hold after Write Strobe (Note 9)
Chip Select Hold after Write Strobe (Note 9)
10
2
110
100
70
2
0
ns
ns
ns
ns
ns
ns
ns
tROLL
Clock rollover to INTR out typically 20 ms
Note 8 Read Strobe width as used in the read timing table is defined as the period when both chip select and read inputs are low Hence read commences when
both signals are low and terminates when either signal returns high
Note 9 Hold time is guaranteed by design but not production tested This limit is not used to calculate outgoing quality levels
Note 10 Write Strobe width as used in the write timing table is defined as the period when both chip select and write inputs are low Hence write commences when
both signals are low and terminates when either signal returns high
AC Test Conditions
Input Pulse Levels
Input Rise and Fall Times
Input and Output
Reference Levels
TRI-STATE Reference
Levels (Note 12)
GND to 3 0V
6 ns (10%–90%)
1 3V
Active High a0 5V
Active Low b0 5V
Note 11 CL e 100 pF includes jig and scope capacitance
Note 12 S1 e VCC for active low to high impedance measurements
S1 e GND for active high to high impedance measurements
S1 e open for all other timing measurements
Capacitance (TA e 25 C f e 1 MHz)
Symbol
Parameter
(Note 13)
Typ Units
CIN Input Capacitance 5 pF
COUT
Output Capacitance
7
pF
Note 13 This parameter is not 100% tested
Note 14 Output rise and fall times 25 ns max (10%–90%) with 100 pF load
TL F 11418 – 2
3

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Timing Waveforms
Read Timing Diagram
Write Timing Diagram
TL F 11418 – 3
Pin Description
CS RD WR (Inputs) These pins interface to mP control
lines The CS pin is an active low enable for the read and
write operations Read and Write pins are also active low
and enable reading or writing to the RTC All three pins are
disabled when power failure is detected However if a read
or write is in progress at this time it will be allowed to com-
plete its cycle
A0 – A4 (Inputs) These 5 pins are for register selection
They individually control which location is to be accessed
These inputs are disabled when power failure is detected
OSC IN (Input) OSC OUT (Output) These two pins are
used to connect the crystal to the internal parallel resonant
oscillator The oscillator is always running when power is
applied to VBB and VCC
MFO (Output) The multi-function output can be used as a
second interrupt (Power fail) output for interrupting the mP
This pin can also provide an output for the oscillator The
MFO output is configured as push-pull active high for nor-
mal or single power supply operation and as an open drain
during standby mode (VBB l VCC) If in battery backed
mode and a pull-up resistor is attached it should be con-
nected to a voltage no greater than VBB
INTR (Output) The interrupt output is used to interrupt the
processor when a timing event or power fail has occurred
and the respective interrupt has been enabled The INTR
TL F 11418 – 4
output is permanently configured active low open drain If in
battery backed mode and a pull-up resistor is attached it
should be connected to a voltage no greater than VBB
D0 – D7 (Input Output) These 8 bidirectional pins connect
to the host mP’s data bus and are used to read from and
write to the RTC When the PFAIL pin goes low and a write
is not in progress these pins are at TRI-STATE
PFAIL (Input) In battery backed mode this pin can have a
digital signal applied to it via some external power detection
logic When PFAIL e logic 0 the RTC goes into a lockout
mode in a minimum of 30 ms or a maximum of 63 ms unless
lockout delay is programmed In the single power supply
mode this pin is not useable as an input and should be tied
to VCC Refer to section on Power Fail Functional Descrip-
tion
VBB (Battery Power Pin) This pin is connected to a back-
up power supply This power supply is switched to the inter-
nal circuitry when the VCC becomes lower than VBB Utiliz-
ing this pin eliminates the need for external logic to switch in
and out the back-up power supply If this feature is not to be
used then this pin must be tied to ground the RTC pro-
grammed for single power supply only and power applied to
the VCC pin
VCC This is the main system power pin
GND This is the common ground power pin for both VBB
and VCC
4

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Connection Diagrams
In-Line Packages
Plastic Chip Carrier
Top View
TL F 11418 – 5
DIP Order Number LV8573AN
See NS Package Number N24C
SOIC Order Number LV8573AM
See NS Package Number M24B
Functional Description
The LV8573A contains a fast access real time clock inter-
rupt control logic and power fail detect logic All functions of
the RTC are controlled by a set of seven registers A simpli-
fied block diagram that shows the major functional blocks is
given in Figure 1
The blocks are described in the following sections
1 Real Time Clock
2 Oscillator Prescaler
3 Interrupt Logic
4 Power Failure Logic
5 Additional Supply Management
The memory map of the RTC is shown in the memory ad-
dressing table (Figure 2) A control bit in the Main Status
Register is used to select either control register block
INITIAL POWER-ON of BOTH VBB and VCC
VBB and VCC may be applied in any sequence In order for
the power fail circuitry to function correctly whenever power
is off the VCC pin must see a path to ground through a
maximum of 1 MX The user should be aware that the con-
trol registers will contain random data The user should en-
sure that the RTC is not in test mode (see register descrip-
tions)
REAL TIME CLOCK FUNCTIONAL DESCRIPTION
As shown in Figure 2 the clock has 8 bytes of counters
which count from 1 100 of a second to years Each counter
counts in BCD and is synchronously clocked The count se-
quence of the individual byte counters within the clock is
shown later in Table VII Note that the day of week day of
month and month counters all roll over to 1 The hours
counter in 12 hour mode rolls over to 1 and the AM PM bit
toggles when the hours rolls over to 12 (AM e 0 PM e 1)
The AM PM bit is bit D7 in the hours counter
All other counters roll over to 0 Upon initial application of
power the counters will contain random information
5
Top View
TL F 11418 – 6
Order Number LV8573AV
See NS Package Number V28A
TL F 11418 – 7
FIGURE 2 LV8573A Internal Memory Map