ST M41T0 User Manual

M41T0

Serial real-time clock

Features

■ Counters for seconds, minutes, hours, day,

date, month, years, and century

■ 32 KHz crystal oscillator integrating load

capacitance (12.5 pF) providing exceptional
oscillator stability and high crystal series
resistance operation

■ Oscillator stop detection monitors clock

operation

■ Serial interface supports I

(400 kHz protocol)

■ Low standby current 0.9 µA (typ at 3 V)

■ 2.0 to 5.5 V clock operating voltage

■ Special software programmable output

■ Operating temperature of –40 to 85 °C

2

C bus

8

1

SO8

June 2011 Doc ID 9105 Rev 7 1/23

www.st.com

1

Contents M41T0

Contents

1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1 2-wire bus characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.1 Bus not busy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.2 Start data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.3 Stop data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.4 Data valid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1.5 Acknowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 READ mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.3 WRITE mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3 Clock operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1 Output driver pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 Oscillator stop detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3 Initial power-on defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5 DC and AC parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

6 Package mechanical information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

7 Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2/23 Doc ID 9105 Rev 7

M41T0 List of tables

List of tables

Table 1. Signal names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Table 2. AC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Table 3. Register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 4. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 5. Operating and AC measurement conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 6. Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 7. DC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 8. Crystal electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 9. SO8 – 8-lead plastic small outline, 150 mils body width, package mechanical data . . . . . 18

Table 10. Carrier tape dimensions for SO8 package (150 mils body width) . . . . . . . . . . . . . . . . . . . . 19

Table 11. Reel dimensions for 12 mm carrier tape - SO8 package (150 mils body width) . . . . . . . . . 20

Table 12. Ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Table 13. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Doc ID 9105 Rev 7 3/23

List of figures M41T0

List of figures

Figure 1. Logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 2. SOIC connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 3. Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 4. Serial bus data transfer sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 5. Acknowledgement sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 6. Bus timing requirements sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 7. Slave address location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 8. READ mode sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 9. Alternate READ mode sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 10. WRITE mode sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 11. AC testing input/output waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 12. SO8 – 8-lead plastic small outline, 150 mils body width, package mechanical drawing. . . 18

Figure 13. Carrier tape for SO8 package (150 mils body width) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 14. Reel schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4/23 Doc ID 9105 Rev 7

M41T0 Description

1 Description

The M41T0 real-time clock is a low power serial real-time clock with a built-in 32.768 kHz
oscillator (external crystal controlled). Eight registers are used for the clock/calendar
function and are configured in binary coded decimal (BCD) format. Addresses and data are
transferred serially via a two-line bidirectional bus. The built-in address register is
incremented automatically after each WRITE or READ data byte.

The M41T0 is supplied in 8-lead plastic small outline package.

Figure 1. Logic diagram

V

CC

OSCI

SCL

Figure 2. SOIC connections

OSCI V

(1)

NF

SS

1. NF pin must be tied to VSS.

Table 1. Signal names

OSCI Oscillator input

OCSO Oscillator output

M41T0

V

SS

1
2
3
4

M41T0

8
7
6
5

AI07029

OSCO

SDA

OUT

AI07028

CC

OUTOSCO
SCL
SDAV

OUT Output driver (open drain)

SDA Serial data address input / output

SCL Serial clock

(1)

NF

V

CC

V

SS

1. NF pin must be tied to VSS.

No function

Supply voltage

Ground

Doc ID 9105 Rev 7 5/23

Description M41T0

Figure 3. Block diagram

OSCI

OSCO

OSCILLATOR

32.768 kHz

DIVIDER

1 Hz

SECONDS

MINUTES

OUT

V

CC

V

SS

SCL

SDA

SERIAL

BUS

INTERFACE

CONTROL

LOGIC

ADDRESS

REGISTER

CENTURY/HOURS

DAY

DATE

MONTH

YEAR

CONTROL

AI07030

6/23 Doc ID 9105 Rev 7

M41T0 Operation

2 Operation

The M41T0 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 8 bytes
contained in the device can then be accessed sequentially in the following order:

1. Seconds register

2. Minutes register

3. Century/hours register

4. Day register

5. Date register

6. Month register

7. Years register

8. Control register

2.1 2-wire bus characteristics

This bus is intended for communication between different ICs. It consists of two lines: one
bidirectional for data signals (SDA) and one for clock signals (SCL). Both the SDA and the
SCL lines must be connected to a positive supply voltage via a pull-up resistor.

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:

2.1.1 Bus not busy

Both data and clock lines remain high.

2.1.2 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.

2.1.3 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.

Doc ID 9105 Rev 7 7/23