M41T256Y
256 Kbit (32K x8) Serial RTC
FEATURES SUMMARY
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5V OPERATING VOLTAGE
SERIAL INTERFACE SUPPORTS
EXTENDED I
2
C BUS ADDRESSING
(400kHz)
AUTOMATIC SWITCH-OVER AND
DESELECT CIRCUITRY
POWER-FAIL DESELECT VOLTAGES:
– M41T256Y: V
CC
= 4.5 to 5.5V;
V
PFD
= 4.2 < V
PFD
< 4.5V
COUNTERS FOR TENTHS/HUNDREDTHS
OF SECONDS, SECONDS, MINUTES,
HOURS, DAY, DATE, MONTH, and YEAR
PROGRAMMABLE SOFTWARE CLOCK
CALIBRATION
32,752 BYTES OF GENERAL PURPOSE
RAM
MICROPROCESSOR POWER-ON RESET
HOLDS MICROPROCESSOR IN RESET
UNTIL SUPPLY VOLTAGE REACHES
STABLE OPERATING LEVEL
AUTOMATIC ADDRESS-INCREMENTING
TAMPER INDICATION CIRCUIT WITH TIME-
STAMP
SLEEP MODE FUNCTION
PACKAGING INCLUDES A 44-LEAD SOIC
AND SNAPHAT
®
TOP (to be ordered
separately)
SOIC PACKAGE PROVIDES DIRECT
CONNECTION FOR A SNAPHAT
®
TOP
WHICH CONTAINS THE BATTERY AND
CRYSTAL
Figure 1. 44-pin, Hatless SOIC Package
44
1
SO44 (MT)
Figure 2. 44-pin SOIC Package
SNAPHAT (SH)
Crystal/Battery
44
1
SOH44 (MH)
June 2004
1/27
M41T256Y
TABLE OF CONTENTS
FEATURES SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 1. 44-pin, Hatless SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2. 44-pin SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
SUMMARY DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Figure 3.
Table 1.
Figure 4.
Figure 5.
Figure 6.
Logic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Signal Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
44-pin SOIC Connections (MT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
44-pin SOIC (MH - SNAPHAT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
OPERATING MODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2-Wire Bus Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Bus not busy.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Start data transfer.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Stop data transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Data Valid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Acknowledge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 7. Serial Bus Data Transfer Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 8. Acknowledgement Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 9. Bus Timing Requirements Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 2. AC Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
READ Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 10.Slave Address Location. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 11.READ Mode Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 12.Alternate READ Mode Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
WRITE Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 13.WRITE Mode Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Data Retention Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Sleep Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
CLOCK OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Reading the Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Setting the Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Stopping and Starting the Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 3. TIMEKEEPER® Register Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Power-on Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Tamper Indication Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Tamper Event Time-Stamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Calibrating the Clock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 14.Crystal Accuracy Across Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 15.Clock Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Battery Low Warning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2/27
M41T256Y
Preferred Power-on/Battery Attach Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Table 4. Preferred Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
MAXIMUM RATING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table 5. Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
DC AND AC PARAMETERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 6. DC and AC Measurement Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 16.AC Testing Input/Output Waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 7. Capacitance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 8. DC Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 9. Crystal Electrical Characteristics (Externally Supplied) . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 17.Power Down/Up Mode AC Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Table 10. Power Down/Up AC Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
PACKAGE MECHANICAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 18.SOH44 – 44-lead Plastic, Hatless, Small Package Outline. . . . . . . . . . . . . . . . . . . . . . . 22
Table 11. SOH44 – 44-lead Plastic, Hatless, Small Package Mechanical Data . . . . . . . . . . . . . . . 22
Figure 19.SOH44 – 44-lead Plastic Small Outline, SNAPHAT, Package Outline . . . . . . . . . . . . . . 23
Table 12. SOH44 – 44-lead Plastic Small Outline, SNAPHAT, Package Mechanical Data . . . . . . 23
Figure 20.SH – 4-pin SNAPHAT Housing for 120mAh Battery & Crystal Outline . . . . . . . . . . . . . . 24
Table 13. SH – 4-pin SNAPHAT Housing for 120mAh Battery & Crystal, Mechanical Data . . . . . . 24
PART NUMBERING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Table 14. Ordering Information Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Table 15. SNAPHAT® Battery Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
REVISION HISTORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Table 16. Document Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3/27
M41T256Y
SUMMARY DESCRIPTION
The M41T256Y Serial TIMEKEEPER
®
SRAM is a
low power 256 Kbit static CMOS SRAM organized
as 32K words by 8 bits. A built-in 32.768kHz oscil-
lator (external crystal controlled) and 8 bytes of the
SRAM (see
Table 3., page 14)
are used for the
clock/calendar function and are configured in bina-
ry coded decimal (BCD) format.
Addresses and data are transferred serially via a
two line, bi-directional I
2
C interface. The built-in
address register is incremented automatically af-
ter each WRITE or READ data byte.
The M41T256Y has a built-in power sense circuit
which detects power failures and automatically
switches to the battery supply when a power fail-
ure occurs. The energy needed to sustain the
SRAM and clock operations can be supplied by a
lithium button-cell supply when a power failure oc-
curs. Functions available to the user include a
non-volatile, time-of-day clock/calendar, and Pow-
er-on Reset. The eight clock address locations
contain the year, month, date, day, hour, minute,
second, and tenths/hundredths of seconds in 24-
hour BCD format. Corrections for 28, 29 (leap year
- valid until year 2100), 30 and 31 day months are
made automatically. The first clock address loca-
tion (7FF8h) stores the clock software calibration
settings as well as the Write Clock Bit.
The M41T256Y is supplied in a 44-lead SOIC
SNAPHAT
®
package (MH - which integrates both
crystal and battery in a single SNAPHAT top) or a
44-pin “hatless” SOIC (MT). The 44-pin, 330mil
SOIC provides sockets with gold-plated contacts
at both ends for direct connection to a separate
SNAPHAT housing containing the battery and
crystal. The unique design allows the SNAPHAT
battery/crystal package to be mounted on top of
the SOIC package after the completion of the sur-
face-mount process.
Insertion of the SNAPHAT housing after reflow
prevents potential battery and crystal damage due
to the high temperatures required for device sur-
face-mounting. The SNAPHAT housing is also
keyed to prevent reverse insertion. The 44-pin
SOIC and crystal/battery packages are shipped
separately in plastic, anti-static tubes or in Tape &
Reel form. For the 44-lead SOIC, the battery/crys-
tal package (e.g., SNAPHAT) part number is
“M4Txx-BR12SH” (see
Table 15., page 25).
Caution:
Do not place the SNAPHAT battery/crys-
tal top in conductive foam, as this will drain the lith-
ium, button-cell battery.
Figure 3. Logic Diagram
VCC VBAT(1)
Table 1. Signal Names
XI
(1)
XO
(1)
Oscillator Input
Oscillator Output
Frequency Test (Open drain)
Reset Output (Open drain)
Serial Clock Input
Serial Data Input/Output
Supply Voltage
Battery Supply Voltage
Ground
Tamper Input
XI(1)
XO(1)
RST
SCL
SDA
M41T256Y
FT
FT
RST
SCL
SDA
V
CC
TP
V
BAT(1)
V
SS
VSS
AI04754b
TP
Note: 1. For 44-pin SNAPHAT (MT) package only.
Note: 1. For 44-pin SNAPHAT (MT) package only.
4/27
M41T256Y
Figure 4. 44-pin SOIC Connections (MT)
XO
XI
NF
RST
NF
NF
NF
NF
NF
NF
NF
TP
NC
NF
NF
NF
NF
SDA
VSS
VSS
NC
VSS
44
1
2
43
3
42
4
41
40
5
39
6
7
38
8
37
36
9
35
10
11 M41T256Y 34
33
12
13
32
14
31
15
30
16
29
17
28
27
18
26
19
20
25
21
24
23
22
VCC
NC
NC
NC
FT
NF
NF
NF
NF
NF
NF
NC
NC
NF
SCL
NC
NF
NF
NF
NF
NF
BAT+
AI04755b
Figure 5. 44-pin SOIC (MH - SNAPHAT)
NC
NC
NF
RST
NF
NF
NF
NF
NF
NF
NF
TP
NC
NF
NF
NF
NF
SDA
VSS
VSS
NC
VSS
44
1
2
43
3
42
4
41
40
5
39
6
7
38
8
37
36
9
35
10
11 M41T256Y 34
33
12
13
32
14
31
15
30
16
29
17
28
27
18
26
19
20
25
21
24
23
22
VCC
NC
NC
NC
FT
NF
NF
NF
NF
NF
NF
NC
NC
NF
SCL
NC
NF
NF
NF
NF
NF
NC
AI07022
Note: No Function (NF) must be tied to V
SS
.
Figure 6. Block Diagram
PULL-UP TO
CHIP VCC
SDA
I2C
INTERFACE
SCL
REAL TIME CLOCK
CALENDAR
32,752 BYTES
USER RAM
RTC
& CALIBRATION
TAMPER BIT
FT(1)
Crystal
32KHz
OSCILLATOR
TP
VCC
POWER
VBAT
VBL= 2.5V
COMPARE
BL
VSO = VBAT
VPFD = 4.38V
COMPARE
COMPARE
POR
RST(1)
AI04759
Note: 1. Open drain output
5/27
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