M41T81SM6E - STMICROELECTRONICS

This is information on a product in full production.

May 2012 Doc ID 10773 Rev 7 1/32

M41T81S

Serial access real-time clock (RTC) with alarms

Datasheet − production data

Features

■Counters for tenths/hundredths of seconds,

seconds, minutes, hours, day, date, month,

year, and century

■32 KHz crystal oscillator with integrated load

capacitance (12.5 pf) which provides

exceptional oscillator stability and high crystal

series resistance operation)

■Oscillator stop detection (monitors clock

operation)

■Serial interface supports I2C bus (400 kHz

protocol)

■Ultra-low battery supply current of 0.6 µA (typ)

■2.0 to 5.5 V clock operating voltage

■Automatic switchover and deselect circuitry

(fixed reference) which provides full operation

in 3.0 V applications)

■VCC = 2.7 to 5.5 V

■2.5 V ≤ VPFD ≤ 2.7 V

■Power-down time-stamp (HT bit) which allows

determination of time elapsed in battery

backup

■Battery low flag

■Programmable alarm and interrupt function

(valid even during battery backup mode)

■Accurate programmable watchdog timer (from

62.5 ms to 128 s)

■Software clock calibration (to compensate for

crystal deviation due to temperature)

■Operating temperature of –40 to 85 °C

■Package options include an 8-lead SOIC or

18-lead embedded crystal SOIC

SO8

8-pin SOIC

SOX18

18-pin (300 mil) SOIC

with embedded crystal

www.st.com

Contents M41T81S
2/32 Doc ID 10773 Rev 7
Contents
1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Operation  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2-wire bus characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
Bus not busy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
Start data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
Stop data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
Data valid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
Acknowledge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
READ mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
WRITE mode  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
Data retention mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
3 Clock operation  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Power-down time-stamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
Clock registers  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
Calibrating the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
Setting alarm clock registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  17
Watchdog timer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  19
Square wave output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  20
Century bit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  20
Battery low warning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
Oscillator fail detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
Oscillator fail interrupt enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
Output driver pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  22
Preferred initial power-on default . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  22
4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5 DC and AC parameters  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6 Package mechanical data  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

M41T81S Contents

Doc ID 10773 Rev 7 3/32

7 Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

List of tables M41T81S
4/32 Doc ID 10773 Rev 7
List of tables
Table 1. Signal names  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Table 2. Clock register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Table 3. Alarm repeat modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 4. Square wave output frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 5. Preferred default values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 6. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Table 7. Operating and AC measurement conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Table 8. Capacitance  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Table 9. DC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Table 10. Crystal electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Table 11. Power down/up AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Table 12. Power down/up trip points DC characteristics  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Table 13. AC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Table 14. SO8 – 8-lead plastic small outline (150 mils body width), package mechanical data. . . . . 28
Table 15. SOX18 – 18-lead plastic small outline, 300 mils, embedded crystal, 
package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Table 16. Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

M41T81S List of figures
Doc ID 10773 Rev 7 5/32
List of figures
Figure 1. Logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 2. 8-pin SOIC (M) connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 3. 18-pin, 300 mil SOIC (MY) connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 4. Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 5. Serial bus data transfer sequence  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 6. Acknowledgement sequence  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 7. Slave address location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 8. READ mode sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 9. Alternative READ mode sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 10. WRITE mode sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 11. Crystal accuracy across temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 12. Clock calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 13. Alarm interrupt reset waveform. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 14. Backup mode alarm waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 15. AC measurement I/O waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 16. Power down/up mode AC waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 17. Bus timing requirements sequence  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 18. SO8 – 8-lead plastic small package outline  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 19. SOX18 – 18-lead plastic small outline, 300 mils, embedded crystal, outline . . . . . . . . . . . 29

Description M41T81S

6/32 Doc ID 10773 Rev 7

1 Description

The M41T81S is a low-power serial real-time clock (RTC) with a built-in 32.768 kHz

oscillator (external crystal controlled). Eight bytes of the SRAM are used for the

clock/calendar function and are configured in binary-coded decimal (BCD) format. An

additional 12 bytes of SRAM provide status/control of alarm, watchdog and square wave

functions. Addresses and data are transferred serially via a two line, bidirectional I2C

interface. The built-in address register is incremented automatically after each WRITE or

READ data byte.

The M41T81S has a built-in power sense circuit which detects power failures and

automatically switches to the battery supply when a power failure occurs. The energy

needed to sustain the clock operations can be supplied by a small lithium button supply

when a power failure occurs. Functions available to the user include a non-volatile, time-of-

day clock/calendar, alarm interrupts, watchdog timer and programmable square wave

output. The eight clock address locations contain the century, year, month, date, day, hour,

minute, second and tenths/hundredths of a second in 24-hour BCD format. Corrections for

28, 29 (leap year - valid until year 2100), 30 and 31 day months are made automatically.

The M41T81S is supplied in either an 8-pin SOIC or an 18-pin 300 mil SOIC package which

includes an embedded 32 KHz crystal.

The 18-pin, embedded crystal SOIC requires only a user-supplied battery to provide non-

volatile operation.

Figure 1. Logic diagram

1. For SO8 package only

SCL

VCC

M41T81S

VSS

SDA

IRQ/FT/OUT/SQW

VBAT

XI(1)

XO(1)

AI09160

M41T81S Description

Doc ID 10773 Rev 7 7/32

Table 1. Signal names

Figure 2. 8-pin SOIC (M) connections

1. Open drain output

Figure 3. 18-pin, 300 mil SOIC (MY) connections

1. NC and NF pins should be tied to VSS. Pins 2 and 3 are internally shorted together. Pins 17 and 16 are

internally shorted together.

2. Open drain output

XI(1)

1. For SO8 package only.

Oscillator input

XO(1) Oscillator output

IRQ/OUT/FT/SQW Interrupt / output driver / frequency test / square wave (open drain)

SDA Serial data input/output

SCL Serial clock input

VBAT Battery supply voltage

VCC Supply voltage

VSS Ground

NC(2)

2. NC and NF pins should be tied to VSS.

No connect

NF(2) No function

IRQ/FT/OUT/SQW(1)

SDA

VBAT SCL

VSS

XI VCC

M41T81S

AI09161

NF(1)

SCL

SDA

VSS

VBAT

NF(1)

VCC

M41T81S

IRQ/FT/OUT/SQW(2)

NF(1)

AI09162

Description M41T81S

8/32 Doc ID 10773 Rev 7

Figure 4. Block diagram

1. Open drain output

2. Square wave function has the highest priority on IRQ/FT/OUT/SQW output.

REAL TIME CLOCK

CALENDAR

RTC W/ALARM

& CALIBRATION

WATCHDOG

OSCILLATOR FAIL

CIRCUIT

SQUARE WAVE

FREQUENCY TEST

OUTPUT DRIVER

IRQ/FT/OUT/SQW(1)

INTERNAL

POWER

SQWE(2)

AFE

SDA

SCL

VCC

OFIE

COMPARE

I2C

INTERFACE

32KHz

OSCILLATOR

VBAT

CRYSTAL

VSO

VPFD

AI09163

WRITE

PROTECT

OUT

M41T81S Operation

Doc ID 10773 Rev 7 9/32

2 Operation

The M41T81S clock operates as a slave device on the serial bus. Access is obtained by

implementing a start condition followed by the correct slave address (D0h). The 20 bytes

contained in the device can then be accessed sequentially in the following order:

1. Tenths/hundredths of a second register

2. Seconds register

3. Minutes register

4. Century/hours register

5. Day register

6. Date register

7. Month register

8. Year register

9. Calibration register

10. Watchdog register

11 - 15. Alarm registers

16. Flags register

17 - 19. Reserved

20. Square wave register

The M41T81S clock continually monitors VCC for an out-of-tolerance condition. Should VCC

fall below VPFD, the device terminates an access in progress and resets the device address

counter. Inputs to the device will not be recognized at this time to prevent erroneous data

from being written to the device from a an out-of-tolerance system. Once VCC falls below the

switchover voltage (VSO), the device automatically switches over to the battery and powers

down into an ultra-low current mode of operation to preserve battery life. If VBAT is less than

VPFD, the device power is switched from VCC to VBAT when VCC drops below VBAT

. If VBAT is

greater than VPFD, the device power is switched from VCC to VBAT when VCC drops below

VPFD. Upon power-up, the device switches from battery to VCC at VSO. When VCC rises

above VPFD, it will recognize the inputs.

For more information on battery storage life refer to application note AN1012, "Predicting the

battery life and data retention period of NVRAMs and serial RTCs" .

2-wire bus characteristics

The bus is intended for communication between different ICs. It consists of two lines: a bi-

directional data signal (SDA) and a clock signal (SCL). Both the SDA and SCL lines must be

connected to a positive supply voltage via a pull-up resistor.

Operation M41T81S

10/32 Doc ID 10773 Rev 7

The following protocol has been defined:

●Data transfer may be initiated only when the bus is not busy.

●During data transfer, the data line must remain stable whenever the clock line is high.

●Changes in the data line, while the clock line is high, will be interpreted as control

signals.

Accordingly, the following bus conditions have been defined:

Bus not busy

Both data and clock lines remain high.

Start data transfer

A change in the state of the data line, from high to low, while the clock is high, defines the

START condition.

Stop data transfer

A change in the state of the data line, from low to high, while the clock is high, defines the

STOP condition.

Data valid

The state of the data line represents valid data when after a start condition, the data line is

stable for the duration of the high period of the clock signal. The data on the line may be

changed during the low period of the clock signal. There is one clock pulse per bit of data.

Each data transfer is initiated with a start condition and terminated with a stop condition.

The number of data bytes transferred between the start and stop conditions is not limited.

The information is transmitted byte-wide and each receiver acknowledges with a ninth bit.

By definition a device that gives out a message is called “transmitter,” the receiving device

that gets the message is called “receiver.” The device that controls the message is called

“master.” The devices that are controlled by the master are called “slaves.”

Acknowledge

Each byte of eight bits is followed by one acknowledge bit. This acknowledge bit is a low

level put on the bus by the receiver whereas the master generates an extra acknowledge

related clock pulse. A slave receiver which is addressed is obliged to generate an

acknowledge after the reception of each byte that has been clocked out of the slave

transmitter.

The device that acknowledges has to pull down the SDA line during the acknowledge clock

pulse in such a way that the SDA line is a stable low during the high period of the

acknowledge related clock pulse. Of course, setup and hold times must be taken into

account. A master receiver must signal an end of data to the slave transmitter by not

generating an acknowledge on the last byte that has been clocked out of the slave. In this

M41T81S Operation

Doc ID 10773 Rev 7 11/32

case the transmitter must leave the data line high to enable the master to generate the

STOP condition.

Figure 5. Serial bus data transfer sequence

Figure 6. Acknowledgement sequence

READ mode

In this mode the master reads the M41T81S slave after setting the slave address (see

Figure 8 on page 12). Following the WRITE mode control bit (R/W=0) and the acknowledge

bit, the word address 'An' is written to the on-chip address pointer. Next the START condition

and slave address are repeated followed by the READ mode control bit (R/W=1). At this

point the master transmitter becomes the master receiver. The data byte which was

addressed will be transmitted and the master receiver will send an acknowledge bit to the

slave transmitter. The address pointer is only incremented on reception of an acknowledge

clock. The M41T81S slave transmitter will now place the data byte at address An+1 on the

bus, the master receiver reads and acknowledges the new byte and the address pointer is

incremented to “An+2.”

This cycle of reading consecutive addresses will continue until the master receiver sends a

STOP condition to the slave transmitter.

The system-to-user transfer of clock data will be halted whenever the address being read is

a clock address (00h to 07h). The update will resume due to a stop condition or when the

pointer increments to any non-clock address (08h-13h).

AI00587

DATA

CLOCK

DATA LINE

STABLE

DATA VALID

STA R T

CONDITION

CHANGE OF

DATA ALLOWED

STOP

CONDITION

AI00601

DATA OUTPUT

BY RECEIVER

DATA OUTPUT

BY TRANSMITTER

SCL FROM

MASTER

START

CLOCK PULSE FOR

ACKNOWLEDGEMENT

12 89

MSB LSB

Operation M41T81S

12/32 Doc ID 10773 Rev 7

Note: This is true both in READ mode and WRITE mode.

An alternate READ mode may also be implemented whereby the master reads the

M41T81S slave without first writing to the (volatile) address pointer. The first address that is

read is the last one stored in the pointer (see Figure 9 on page 12).

Figure 7. Slave address location

Figure 8. READ mode sequence

Figure 9. Alternative READ mode sequence

AI00602

R/W

SLAVE ADDRESS

STA R T A

0100011

MSB

LSB

AI00899

BUS ACTIVITY:

ACK

NO ACK STOP

START

SDA LINE

BUS ACTIVITY:

MASTER

R/W

DATA n DATA n + 1

DATA n+X

WORD

ADDRESS (An)

SLAVE

ADDRESS

START

R/W

SLAVE

ADDRESS

ACK

AI00895

BUS ACTIVITY:

ACK

NO ACK STOP

STA R T

PSDA LINE

BUS ACTIVITY:

MASTER

R/W

DATA n DATA n+1 DATA n+X

SLAVE

ADDRESS

M41T81S Operation

Doc ID 10773 Rev 7 13/32

WRITE mode

In this mode the master transmitter transmits to the M41T81S slave receiver. Bus protocol is

shown in Figure 10 on page 13. Following the START condition and slave address, a logic '0'

(R/W=0) is placed on the bus and indicates to the addressed device that word address “An”

will follow and is to be written to the on-chip address pointer. The data word to be written to

the memory is strobed in next and the internal address pointer is incremented to the next

address location on the reception of an acknowledge clock. The M41T81S slave receiver

will send an acknowledge clock to the master transmitter after it has received the slave

address see Figure 7 on page 12 and again after it has received the word address and each

data byte.

Data retention mode

With valid VCC applied, the M41T81S can be accessed as described above with READ or

WRITE cycles. Should the supply voltage decay, the power input will be switched from the

VCC pin to the battery when VCC falls below the battery backup switchover voltage (VSO). At

this time the clock registers will be maintained by the attached battery supply. On power-up,

when VCC returns to a nominal value, write protection continues for tREC.

For a further, more detailed review of lifetime calculations, please see application note

AN1012.

Figure 10. WRITE mode sequence

AI00591

BUS ACTIVITY:

ACK

ACK STOP

START

PSDA LINE

BUS ACTIVITY:

MASTER

R/W

DATA n DATA n + 1 DATA n + X

WORD

ADDRESS (An)

SLAVE

ADDRESS

Clock operation M41T81S

14/32 Doc ID 10773 Rev 7

3 Clock operation

The 20-byte register map (see Table 2: Clock register map on page 15) is used to both set

the clock and to read the date and time from the clock, in a binary coded decimal format.

Tenths/hundredths of seconds, seconds, minutes, and hours are contained within the first

four registers.

Note: Tenths/hundredths of seconds cannot be written to any value other than “00.”

Bits D6 and D7 of clock register 03h (century/hours register) contain the CENTURY

ENABLE bit (CEB) and the CENTURY bit (CB). Setting CEB to a '1' will cause CB to toggle,

either from '0' to '1' or from '1' to '0' at the turn of the century (depending upon its initial

state). If CEB is set to a '0,' CB will not toggle. Bits D0 through D2 of register 04h contain the

day (day of week). Registers 05h, 06h, and 07h contain the date (day of month), month and

years. The ninth clock register is the calibration register (this is described in the clock

calibration section). Bit D7 of register 01h contains the STOP bit (ST). Setting this bit to a '1'

will cause the oscillator to stop. If the device is expected to spend a significant amount of

time on the shelf, the oscillator may be stopped to reduce current drain. When reset to a '0'

the oscillator restarts within one second.

The eight clock registers may be read one byte at a time, or in a sequential block. Provision

has been made to assure that a clock update does not occur while any of the eight clock

addresses are being read. If a clock address is being read, an update of the clock registers

will be halted. This will prevent a transition of data during the READ.

Power-down time-stamp

When a power failure occurs, the HALT (HT) bit will automatically be set to a '1.' This will

prevent the clock from updating the registers, and will allow the user to read the exact time

of the power-down event. Resetting the HT bit to a '0' will allow the clock to update the

registers with the current time. For more information, please refer to AN1572, “Power-down

time-stamp function in serial real-time clocks (RTCs)”.

Clock registers

The M41T81S offers 20 internal registers which contain clock, alarm, watchdog, flags,

square wave and calibration data. These registers are memory locations which contain

external (user accessible) and internal copies of the data (usually referred to as BiPORT™

cells). The external copies are independent of internal functions except that they are

updated periodically by the simultaneous transfer of the incremented internal copy. The

internal divider (or clock) chain will be reset upon the completion of a WRITE to any clock

address.

The system-to-user transfer of clock data will be halted whenever the address being read is

a clock address (00h to 07h). The update will resume either due to a stop condition or when

the pointer increments to any non-clock address (08h-13h).

Clock and alarm registers store data in BCD. Calibration, watchdog and square wave

registers store data in binary format.

M41T81S Clock operation

Doc ID 10773 Rev 7 15/32

Table 2. Clock register map

0 = Must be set to '0'

ABE = Alarm in battery backup mode enable bit

AF = Alarm flag (read only)

AFE = Alarm flag enable flag

BL = Battery low bit

BMB0-BMB4 = Watchdog multiplier bits

CB = Century bit

CEB = Century enable bit

FT = Frequency test bit

HT = Halt update bit

OF = Oscillator fail flag

OFIE = Oscillator fail interrupt enable

OUT = Output level

RB0-RB1 = Watchdog resolution bits

RPT1-RPT5 = Alarm repeat mode bits

RS0-RS3 = SQW frequency

S = Sign bit

SQWE = Square wave enable

ST = Stop bit

WDF = Watchdog flag (read only)

Addr Function/range BCD

format

D7 D6 D5 D4 D3 D2 D1 D0

00h 0.1 seconds 0.01 Seconds Seconds 00-99

01h ST 10 seconds Seconds Seconds 00-59

02h 0 10 minutes Minutes Minutes 00-59

03h CEB CB 10 hours Hours (24-hour format) Century/hours 0-1/00-23

04h00000 Day of week Day 01-7

05h 0 0 10 date Date: day of month Date 01-31

06h 0 0 0 10M Month Month 01-12

07h 10 years Year Year 00-99

08h OUT FT S Calibration Calibration

09h OFIE BMB4 BMB3 BMB2 BMB1 BMB0 RB1 RB0 Watchdog

0Ah AFE SQW ABE Al Alarm month Al month 01-12

0Bh RPT4 RPT5 AI 10 date Alarm date Al date 01-31

0Ch RPT3 HT AI 10 hour Alarm hour Al hour 00-23

0Dh RPT2 Alarm 10 minutes Alarm minutes Al min 00-59

0Eh RPT1 Alarm 10 seconds Alarm seconds Al sec 00-59

0Fh WDF AF 0 BL 0 OF 0 0 Flags

10h00000000Reserved

11h00000000Reserved

12h00000000Reserved

13h RS3 RS2 RS1 RS0 0 0 0 0 SQW

Clock operation M41T81S

16/32 Doc ID 10773 Rev 7

Calibrating the clock

The M41T81S is driven by a quartz controlled oscillator with a nominal frequency of

32,768 Hz. The devices are tested not exceed ±35 ppm (parts per million) oscillator

frequency error at 25oC, which equates to about +1.9 to –1.1 minutes per month (see

Figure 11 on page 17). When the calibration circuit is properly employed, accuracy improves

to better than ±2 ppm at 25°C.

The oscillation rate of crystals changes with temperature. The M41T81S design employs

periodic counter correction. The calibration circuit adds or subtracts counts from the

oscillator divider circuit at the divide by 256 stage, as shown in Figure 12 on page 17. The

number of times pulses which are blanked (subtracted, negative calibration) or split (added,

positive calibration) depends upon the value loaded into the five calibration bits found in the

calibration register. Adding counts speeds the clock up, subtracting counts slows the clock

down.

The calibration bits occupy the five lower order bits (D4-D0) in the calibration register 08h.

These bits can be set to represent any value between 0 and 31 in binary form. Bit D5 is a

sign bit; '1' indicates positive calibration, '0' indicates negative calibration. Calibration occurs

within a 64 minute cycle. The first 62 minutes in the cycle may, once per minute, have one

second either shortened by 128 or lengthened by 256 oscillator cycles. If a binary '1' is

loaded into the register, only the first 2 minutes in the 64 minute cycle will be modified; if a

binary 6 is loaded, the first 12 will be affected, and so on.

Therefore, each calibration step has the effect of adding 512 or subtracting 256 oscillator

cycles for every 125,829,120 actual oscillator cycles, that is +4.068 or –2.034 ppm of

adjustment per calibration step in the calibration register (see Figure 12 on page 17).

Assuming that the oscillator is running at exactly 32,768Hz, each of the 31 increments in the

Calibration byte would represent +10.7 or –5.35 seconds per month which corresponds to a

total range of +5.5 or –2.75 minutes per month.

Two methods are available for ascertaining how much calibration a given M41T81S may

require.

The first involves setting the clock, letting it run for a month and comparing it to a known

accurate reference and recording deviation over a fixed period of time. Calibration values,

including the number of seconds lost or gained in a given period, can be found in application

note AN934, “TIMEKEEPER® calibration.” This allows the designer to give the end user the

ability to calibrate the clock as the environment requires, even if the final product is

packaged in a non-user serviceable enclosure. The designer could provide a simple utility

that accesses the calibration byte.

The second approach is better suited to a manufacturing environment, and involves the use

of the IRQ/FT/OUT/SQW pin. The pin will toggle at 512 Hz, when the stop bit (ST, D7 of

01h) is '0,' the frequency test bit (FT, D6 of 08h) is '1,' the alarm flag enable bit (AFE, D7 of

0Ah) is '0,' and the square wave enable bit (SQWE, D6 of 0Ah) is '0' and the watchdog

Any deviation from 512 Hz indicates the degree and direction of oscillator frequency shift at

the test temperature. For example, a reading of 512.010124 Hz would indicate a +20 ppm

oscillator frequency error, requiring a –10 (XX001010) to be loaded into the calibration byte

for correction. Note that setting or changing the calibration byte does not affect the

frequency test output frequency.

M41T81S Clock operation

Doc ID 10773 Rev 7 17/32

The IRQ/FT/OUT/SQW pin is an open drain output which requires a pull-up resistor to VCC

for proper operation. A 500-10 k resistor is recommended in order to control the rise time.

The FT bit is cleared on power-down.

Figure 11. Crystal accuracy across temperature

Figure 12. Clock calibration

Setting alarm clock registers

Address locations 0Ah-0Eh contain the alarm settings. The alarm can be configured to go

off at a prescribed time on a specific month, date, hour, minute, or second or repeat every

year, month, day, hour, minute, or second. It can also be programmed to go off while the

M41T81S is in the battery backup mode to serve as a system wake-up call.

Bits RPT5-RPT1 put the alarm in the repeat mode of operation. Table 3 on page 19 shows

the possible configurations. Codes not listed in the table default to the once per second

mode to quickly alert the user of an incorrect alarm setting.

AI07888

–160

0 10203040506070

Frequency (ppm)

Temperature °C

80–10–20–30–40

–100

–120

–140

–40

–60

–80

–20

= –0.036 ppm/°C2 ± 0.006 ppm/°C2

ΔF= K x (T – TO)2

TO = 25°C ± 5°C

AI00594B

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION

Clock operation M41T81S

18/32 Doc ID 10773 Rev 7

When the clock information matches the alarm clock settings based on the match criteria

defined by RPT5-RPT1, the AF (alarm flag) is set. If AFE (alarm flag enable) is also set (and

SQWE is '0.'), the alarm condition activates the IRQ/FT/OUT/SQW pin.

Note: If the address pointer is allowed to increment to the flags register address, an alarm

condition will not cause the Interrupt/Flag to occur until the address pointer is moved to a

different address. It should also be noted that if the last address written is the “Alarm

Seconds,” the address pointer will increment to the flag address, causing this situation to

occur.

The IRQ/FT/OUT/SQW output is cleared by a READ to the flags register as shown in

Figure 13. A subsequent READ of the flags register is necessary to see that the value of the

alarm flag has been reset to '0.'

The IRQ/FT/OUT/SQW pin can also be activated in the battery backup mode. The

IRQ/FT/OUT/SQW will go low if an alarm occurs and both ABE (alarm in battery backup

mode enable) and AFE are set. Figure 14 illustrates the backup mode alarm timing.

Figure 13. Alarm interrupt reset waveform

Figure 14. Backup mode alarm waveform

IRQ/FT/OUT/SQW

ACTIVE FLAG

0Fh0Eh 10h

HIGH-Z

AI04617

IRQ/FT/OUT/SQW

ABE and AFE Bits

AF Bit in Flags

HIGH-Z

PFD

trec

AI09164b

M41T81S Clock operation

Doc ID 10773 Rev 7 19/32

Watchdog timer

The watchdog timer can be used to detect an out-of-control microprocessor. The user

programs the watchdog timer by setting the desired amount of time-out into the watchdog

RB1-RB0 select the resolution, where 00 = 1/16 second, 01 = 1/4 second, 10 = 1 second,

and 11 = 4 seconds. The amount of time-out is then determined to be the multiplication of

the five-bit multiplier value with the resolution. (For example: writing 00001110 in the

watchdog register = 3*1, or 3 seconds). If the processor does not reset the timer within the

specified period, the M41T81S sets the WDF (watchdog flag) and generates a watchdog

interrupt.

The watchdog timer can be reset by having the microprocessor perform a WRITE of the

watchdog register. The time-out period then starts over.

Should the watchdog timer time-out, a value of 00h needs to be written to the watchdog

function until it is again programmed correctly. A READ of the flags register will reset the

watchdog flag (bit D7; register 0Fh).

The watchdog function is automatically disabled upon power-up and the watchdog register

is cleared. If the watchdog function is set, the frequency test function is activated, and the

SQWE bit is '0,' the watchdog function prevails and the frequency test function is denied.

Table 3. Alarm repeat modes

RPT5 RPT4 RPT3 RPT2 RPT1 Alarm setting

1 1 1 1 1 Once per second

1 1 1 1 0 Once per minute

1 1 1 0 0 Once per hour

1 1 0 0 0 Once per day

1 0 0 0 0 Once per month

0 0 0 0 0 Once per year

Clock operation M41T81S

20/32 Doc ID 10773 Rev 7

Square wave output

The M41T81S offers the user a programmable square wave function which is output on the

SQW pin. RS3-RS0 bits located in 13h establish the square wave output frequency. These

frequencies are listed in Ta bl e 4 . Once the selection of the SQW frequency has been

completed, the IRQ/FT/OUT/SQW pin can be turned on and off under software control with

the square wave enable bit (SQWE) located in register 0Ah.

Century bit

Bits D7 and D6 of clock register 03h contain the CENTURY ENABLE bit (CEB) and the

CENTURY bit (CB). Setting CEB to a '1' will cause CB to toggle, either from a '0' to '1' or

from '1' to '0' at the turn of the century (depending upon its initial state). If CEB is set to a '0,'

CB will not toggle.

Table 4. Square wave output frequency

Square wave bits Square wave

RS3 RS2 RS1 RS0 Frequency Units

0000None-

000132.768kHz

0 0 1 0 8.192 kHz

0 0 1 1 4.096 kHz

0 1 0 0 2.048 kHz

0 1 0 1 1.024 kHz

0110512Hz

0111256Hz

1000128Hz

100164Hz

101032Hz

101116Hz

11008Hz

11014Hz

11102Hz

11111Hz

M41T81S Clock operation

Doc ID 10773 Rev 7 21/32

Battery low warning

The M41T81S automatically performs battery voltage monitoring upon power-up and at

factory-programmed time intervals of approximately 24 hours. The battery low (BL) bit, bit

D4 of flags register 0Fh, will be asserted if the battery voltage is found to be less than

approximately 2.5 V. The BL bit will remain asserted until completion of battery replacement

and subsequent battery low monitoring tests, either during the next power-up sequence or

the next scheduled 24-hour interval.

If a battery low is generated during a power-up sequence, this indicates that the battery is

below approximately 2.5 volts and may not be able to maintain data integrity. Clock data

should be considered suspect and verified as correct. A fresh battery should be installed.

If a battery low indication is generated during the 24-hour interval check, this indicates that

the battery is near end of life. However, data is not compromised due to the fact that a

nominal VCC is supplied. In order to insure data integrity during subsequent periods of

battery back-up mode, the battery should be replaced.

The M41T81S only monitors the battery when a nominal VCC is applied to the device. Thus

applications which require extensive durations in the battery backup mode should be

powered-up periodically (at least once every few months) in order for this technique to be

beneficial. Additionally, if a battery low is indicated, data integrity should be verified upon

power-up via a checksum or other technique.

Oscillator fail detection

If the oscillator fail bit (OF) is internally set to '1,' this indicates that the oscillator has either

stopped, or was stopped for some period of time and can be used to judge the validity of the

clock and date data.

In the event the OF bit is found to be set to '1' at any time other than the initial power-up, the

STOP bit (ST) should be written to a '1,' then immediately reset to '0.' This will restart the

oscillator.

The following conditions can cause the OF bit to be set:

●The first time power is applied (defaults to a '1' on power-up).

●The voltage present on VCC is insufficient to support oscillation.

●The ST bit is set to '1.'

●External interference of the crystal.

The OF bit will remain set to '1' until written to logic '0.' The oscillator must start and have

run for at least 4 seconds before attempting to reset the OF bit to '0.'

Oscillator fail interrupt enable

If the oscillator fail interrupt bit (OFIE) is set to a '1,' the IRQ pin will also be activated. The

IRQ output is cleared by resetting the OFIE or OF bit to '0' (not be reading the flags register).

Clock operation M41T81S

22/32 Doc ID 10773 Rev 7

Output driver pin

When the FT bit, AFE bit, SQWE bit, and watchdog register are not set, the

IRQ/FT/OUT/SQW pin becomes an output driver that reflects the contents of D7 of the

calibration register. In other words, when D7 (OUT bit) and D6 (FT bit) of address location

08h are a '0,' then the IRQ/FT/OUT/SQW pin will be driven low.

Note: The IRQ/FT/OUT/SQW pin is an open drain which requires an external pull-up resistor.

Preferred initial power-on default

Upon initial application of power to the device, the following register bits are set to a '0' state:

watchdog register; AFE; ABE; SQWE; OFIE; and FT. The following bits are set to a '1' state:

ST; OUT; OF; and HT (see Ta bl e 5 ).

Table 5. Preferred default values

Condition ST HT Out FT AFE SQWE ABE WATCHDOG

Initial power-up(2) 11100 0 0 0 1 0

Subsequent power-up

(with battery backup)(3) UC 1 UC 0 UC UC UC 0 UC UC

1. BMB0-BMB4, RB0, RB1

2. State of other control bits undefined

3. UC = Unchanged

M41T81S Maximum ratings

Doc ID 10773 Rev 7 23/32

4 Maximum ratings

Stressing the device above the rating listed in the absolute maximum ratings table may

cause permanent damage to the device. These are stress ratings only and operation of the

device at these or any other conditions above those indicated in the operating sections of

this specification is not implied. Exposure to absolute maximum rating conditions for

extended periods may affect device reliability.

Table 6. Absolute maximum ratings

Caution: Negative undershoots below –0.3 volts are not allowed on any pin while in the battery

backup mode.

Sym Parameter Value Unit

TSTG Storage temperature (VCC off, oscillator off) –55 to 125 °C

VCC Supply voltage –0.3 to 7 V

TSLD Lead solder temperature for 10 seconds SO8(1)

1. For SO8 package, Lead-free (Pb-free) lead finish, reflow at peak temperature of 260 °C. The time above

255 °C must not exceed 30 seconds.

260 °C

SOX18(2)

2. For SOX18 package, reflow at peak temperature of 240 °C. The time above 235 °C must not exceed 20

seconds.

240 °C

VIO Input or output voltages –0.3 to VCC + 0.3 V

IOOutput current 20 mA

PDPower dissipation 1 W

DC and AC parameters M41T81S

24/32 Doc ID 10773 Rev 7

5 DC and AC parameters

This section summarizes the operating and measurement conditions, as well as the DC and

AC characteristics of the device. The parameters in the following DC and AC Characteristic

tables are derived from tests performed under the measurement conditions listed in the

relevant tables. Designers should check that the operating conditions in their projects match

the measurement conditions when using the quoted parameters.

Table 7. Operating and AC measurement conditions

Note: Output Hi-Z is defined as the point where data is no longer driven.

Figure 15. AC measurement I/O waveform

Table 8. Capacitance

Parameter M41T81S

Supply voltage (VCC) 2.7 to 5.5 V

Ambient operating temperature (TA) –40 to 85 °C

Load capacitance (CL) 100 pF

Input rise and fall times ≤ 50 ns

Input pulse voltages 0.2VCC to 0.8VCC

Input and output timing ref. voltages 0.3VCC to 0.7VCC

Symbol Parameter(1)(2)

1. Effective capacitance measured with power supply at 5 V; sampled only, not 100% tested.

2. At 25 °C, f = 1 MHz

Min Max Unit

CIN Input capacitance - 7 pF

COUT(3)

3. Outputs deselected

Output capacitance - 10 pF

tLP Low-pass filter input time constant (SDA and SCL) - 50 ns

AI02568

0.8VCC

0.2VCC

0.7VCC

0.3VCC

M41T81S DC and AC parameters

Doc ID 10773 Rev 7 25/32

Table 9. DC characteristics

Table 10. Crystal electrical characteristics

Figure 16. Power down/up mode AC waveforms

Sym Parameter Test condition(1)

1. Valid for ambient operating temperature: TA = –40 to 85 °C; VCC = 2.7 to 5.5 V (except where noted).

Min Typ Max Unit

ILI Input leakage current 0 V ≤ VIN ≤ VCC ±1 µA

ILO Output leakage current 0 V ≤ VOUT ≤ VCC ±1 µA

ICC1 Supply current Switch freq = 400 kHz 400 µA

ICC2 Supply current (standby)

SCL = 0 Hz

All inputs

≥ VCC – 0.2 V

≤ VSS + 0.2 V

100 µA

VIL Input low voltage –0.3 0.3VCC V

VIH Input high voltage 0.7VCC

VCC +

0.3 V

VOL

Output low voltage IOL = 3.0 mA 0.4 V

Output low voltage

(open drain)(2)

2. For IRQ/FT/OUT/SQW pin (open drain)

IOL = 10 mA 0.4 V

Pull-up supply voltage

(open drain) IRQ/OUT/FT/SQW 5.5 V

VBAT(3)

3. STMicroelectronics recommends the RAYOVAC BR1225 or BR1632 (or equivalent) as the battery supply.

Backup supply voltage 2.0 3.5(4)

4. For rechargeable back-up, VBAT (max) may be considered to be VCC.

IBAT Battery supply current TA = 25 °C, VCC = 0 V

Oscillator ON, VBAT = 3 V 0.6 1 µA

Sym Parameter(1)and(2)

1. Externally supplied if using the SO8 package. STMicroelectronics recommends the KDS DT-38:

1TA/1TC252E127, Tuning Fork Type (thru-hole) or the DMX-26S: 1TJS125FH2A212, (SMD) quartz

crystal for industrial temperature operations. KDS can be contacted at kouhou@kdsj.co.jp or

http://www.kdsj.co.jp for further information on this crystal type.

2. Load capacitors are integrated within the M41T81S. Circuit board layout considerations for the 32.768 kHz

crystal of minimum trace lengths and isolation from RF generating signals should be taken into account.

Min Typ Max Units

fOResonant frequency - 32.768 kHz

RSSeries resistance - 60(3)

3. For applications requiring back-up supply operation below 2.5 V, RS (max) should be considered 40 kΩ.

kΩ

CLLoad capacitance - 12.5 pF

AI00596

VCC

trec

tPD

VSO

SDA

SCL DON'T CARE

DC and AC parameters M41T81S

26/32 Doc ID 10773 Rev 7

Table 11. Power down/up AC characteristics

Table 12. Power down/up trip points DC characteristics

Figure 17. Bus timing requirements sequence

Symbol Parameter(1)(2)

1. VCC fall time should not exceed 5 mV/µs.

2. Valid for ambient operating temperature: TA = –40 to 85 °C; VCC = 2.7 to 5.5 V (except where noted).

Min Typ Max Unit

tPD SCL and SDA at VIH before power-down 0 - - nS

trec SCL and SDA at VIH after power-up 10 - - µS

Sym Parameter(1)(2)

1. All voltages referenced to VSS.

2. Valid for ambient operating temperature: TA = –40 to 85 °C; VCC = 2.7 to 5.5 V (except where noted).

Min Typ Max Unit

VPFD

Power-fail deselect 2.5 2.6 2.7 V

Hysteresis 25 mV

VSO

Battery backup switchover voltage

(VCC < VBAT; VCC < VPFD)

VBAT < VPFD VBAT V

VBAT > VPFD VPFD V

Hysteresis 40 mV

AI00589

SDA

tSU:STOtSU:STA

tHD:STA

SCL

tSU:DAT

tHD:DAT

tHIGH

tLOW

tHD:STAtBUF

M41T81S DC and AC parameters

Doc ID 10773 Rev 7 27/32

Table 13. AC characteristics

Sym Parameter(1)

1. Valid for ambient operating temperature: TA = –40 to 85 °C; VCC = 2.7 to 5.5 V (except where noted).

Min Typ Max Units

fSCL SCL clock frequency 0 - 400 kHz

tLOW Clock low period 1.3 - µs

tHIGH Clock high period 600 - ns

tRSDA and SCL rise time - 300 ns

tFSDA and SCL fall time - 300 ns

tHD:STA

START condition hold time

(after this period the first clock pulse is

generated)

600 - ns

tSU:STA

START condition setup time

(only relevant for a repeated start condition) 600 - ns

tSU:DAT Data setup time 100 - ns

tHD:DAT(2)

2. Transmitter must internally provide a hold time to bridge the undefined region (300 ns max) of the falling

edge of SCL.

Data hold time 0 - µs

tSU:STO STOP condition setup time 600 - ns

tBUF

Time the bus must be free before a new

transmission can start 1.3 - µs

Package mechanical data M41T81S

28/32 Doc ID 10773 Rev 7

6 Package mechanical data

In order to meet environmental requirements, ST offers these devices in different grades of

ECOPACK® packages, depending on their level of environmental compliance. ECOPACK®

specifications, grade definitions and product status are available at: www.st.com.

ECOPACK® is an ST trademark.

Figure 18. SO8 – 8-lead plastic small package outline

Note: Drawing is not to scale.

SO-A

ccc

h x 45°

0.25 mm

GAUGE PLANE

Table 14. SO8 – 8-lead plastic small outline (150 mils body width), package

mechanical data

Symb

mm inches

Typ Min Max Typ Min Max

A1.750.069

A1 0.10 0.25 0.004 0.010

A2 1.25 0.049

b 0.28 0.48 0.011 0.019

c 0.17 0.23 0.007 0.009

ccc 0.10 0.004

D 4.90 4.80 5.00 0.193 0.189 0.197

E 6.00 5.80 6.20 0.236 0.228 0.244

E1 3.90 3.80 4.00 0.154 0.150 0.157

e 1.27 0.050

h 0.25 0.50 0.010 0.020

k0°8°0°8°

L 0.40 0.127 0.016 0.050

L1 1.04 0.041

M41T81S Package mechanical data

Doc ID 10773 Rev 7 29/32

Figure 19. SOX18 – 18-lead plastic small outline, 300 mils, embedded crystal, outline

Note: Drawing is not to scale.

SOX18

Table 15. SOX18 – 18-lead plastic small outline, 300 mils, embedded crystal,

package mechanical data

Symbol

millimeters inches

Typ Min Max Typ Min Max

A 2.57 2.44 2.69 0.101 0.096 0.106

A1 0.23 0.15 0.31 0.009 0.006 0.012

A2 2.34 2.29 2.39 0.092 0.090 0.094

B 0.46 0.41 0.51 0.018 0.016 0.020

c 0.25 0.20 0.31 0.010 0.008 0.012

D 11.61 11.56 11.66 0.457 0.455 0.459

E 7.62 7.57 7.67 0.300 0.298 0.302

E1 10.34 10.16 10.52 0.407 0.400 0.414

e1.27 0.050

L 0.66 0.51 0.81 0.026 0.020 0.032

Part numbering M41T81S

30/32 Doc ID 10773 Rev 7

7 Part numbering

For other options, or for more information on any aspect of this device, please contact the

ST sales office nearest you.

Table 16. Ordering information

Example: M41T 81S M 6 F

Device type

M41T

Supply voltage and write protect voltage

81S = VCC = 2.7 to 5.5 V

Package

M = SO8

MY(1) = SOX18

1. The SOX18 package includes an embedded 32,768 Hz crystal. Contact local ST sales office for

availability.

Temperature range

6 = –40 °C to 85 °C

Shipping method

E = ECOPACK® package, tubes(2)

2. Shipment in tubes is not recommended for new design. Contact local ST sales office for availability.

F = ECOPACK® package, tape & reel

M41T81S Revision history
Doc ID 10773 Rev 7 31/32
8 Revision history
Date Revision Changes
22-Jan-2004 0.1 First draft
06-Feb-2004 0.2 Update BL information, characteristics, ratings, and Lead (Pb)-free information 
(Ta b l e 1 2 , Ta bl e 6 , Ta b l e 1 0 , Ta b le 1 6 )
20-Feb-2004 0.3 Update characteristics (Ta b l e 1 1 , Ta b le 1 2 , Ta bl e 7 , Part numbering)
14-Apr-2004 1 Product promoted; reformatted; update characteristics, including Lead-free 
package information (Figure 3, Figure 4, Figure 11, Figure 14; Ta b l e 1 3 , Ta bl e 1 6 )
05-May-2004 1.1 Update DC characteristics (Ta b l e 9 )
16-Jun-2004 1.2 Add shipping package (Ta b l e 1 6 )
13-Sep-2004 2 Update maximum ratings (Ta b l e 6 )
26-Nov-2004 3 Promote document; update characteristics and marketing status (cover page, 
Figure 5)
23-Sep-2005 4 Update features; added Lead-free information (cover page; Figure 4)
22-Jan-2007 5 Remove TIMEKEEPER references and update package mechanical data 
(Figure 18 and Figure 19)
13-Sep-2010 6 Updated Section 4, ECOPACK® text in Section 6; reformatted document.
16-May-2012 7 Added reference to AN1572 in Power-down time-stamp on page 14; updated 
footnote 1 of Ta b l e 6 ; updated Table 16: Ordering information.

M41T81S

32/32 Doc ID 10773 Rev 7

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