M41ST85Y
M41ST85W
5.0 or 3.0V, 512 bit (64 x 8)
Serial RTC and NVRAM Supervisor
FEATURES SUMMARY
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5.0 OR 3.0V OPERATING VOLTAGE
SERIAL INTERFACE SUPPORTS I
2
C BUS
(400 KHz)
NVRAM SUPERVISOR FOR EXTERNAL
LPSRAM
OPTIMIZED FOR MINIMAL
INTERCONNECT TO MCU
2.5 TO 5.5V OSCILLATOR OPERATING
VOLTAGE
AUTOMATIC SWITCH-OVER AND
DESELECT CIRCUITRY
CHOICE OF POWER-FAIL DESELECT
VOLTAGES
– M41ST85Y: V
CC
= 4.5 to 5.5V;
4.20V
≤
V
PFD
≤
4.50V
– M41ST85W: V
CC
= 2.7 to 3.6V;
2.55V
≤
V
PFD
≤
2.70V
1.25V REFERENCE (for PFI/PFO)
COUNTERS FOR TENTHS/HUNDREDTHS
OF SECONDS, SECONDS, MINUTES,
HOURS, DAY, DATE, MONTH, YEAR, AND
CENTURY
44 BYTES OF GENERAL PURPOSE RAM
PROGRAMMABLE ALARM AND
INTERRUPT FUNCTION (VALID EVEN
DURING BATTERY BACK-UP MODE)
WATCHDOG TIMER
MICROPROCESSOR POWER-ON RESET
BATTERY LOW FLAG
POWER-DOWN TIMESTAMP (HT BIT)
ULTRA-LOW BATTERY SUPPLY CURRENT
OF 500nA (MAX)
PACKAGING INCLUDES A 28-LEAD SOIC
AND SNAPHAT
®
TOP (to be ordered
separately)
SOIC SNAPHAT PACKAGE PROVIDES
DIRECT CONNECTION FOR A SNAPHAT
TOP WHICH CONTAINS THE BATTERY
AND CRYSTAL
SOIC EMBEDDED CRYSTAL PACKAGE
(MX) OPTION
Figure 1. 28-pin SOIC Package
SNAPHAT (SH)
Battery & Crystal
28
1
SOH28 (MH)
Figure 2. 28-pin (300mil) SOIC Package
EMBEDDED Crystal
SOX28 (MX)
September 2004
1/34
M41ST85Y, M41ST85W
TABLE OF CONTENTS
FEATURES SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 1. 28-pin SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2. 28-pin (300mil) SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
SUMMARY DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Figure 3.
Table 1.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Logic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Signal Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28-pin SOIC Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28-pin, 300mil SOIC (MX) Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hardware Hookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
......
......
......
......
......
......
.....5
.....5
.....5
.....5
.....6
.....7
OPERATING MODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2-Wire Bus Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 8. Serial Bus Data Transfer Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 9. Acknowledgement Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 10.WRITE Cycle Timing: RTC & External SRAM Control Signals . . . . . . . . . . . . . . . . . . . . . 9
READ Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 11.Slave Address Location. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 12.READ Mode Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 13.Alternate READ Mode Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
WRITE Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 14.WRITE Mode Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Data Retention Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
CLOCK OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Power-down Time-Stamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
TIMEKEEPER
®
Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 2. TIMEKEEPER
®
Register Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Calibrating the Clock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 15.Crystal Accuracy Across Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 16.Calibration Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Setting Alarm Clock Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 17.Alarm Interrupt Reset Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Table 3. Alarm Repeat Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 18.Back-Up Mode Alarm Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Watchdog Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Square Wave Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 4. Square Wave Output Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Power-on Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Reset Inputs (RSTIN1 & RSTIN2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 19.RSTIN1 & RSTIN2 Timing Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 5. Reset AC Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
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M41ST85Y, M41ST85W
Power-fail INPUT/OUTPUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Century Bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Output Driver Pin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Battery Low Warning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
t
rec
Bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Initial Power-on Defaults. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 6. t
rec
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 7. Default Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
MAXIMUM RATING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Table 8. Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
DC and AC PARAMETERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Table 9. DC and AC Measurement Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 20.AC Testing Input/Output Waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Table 10. Capacitance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Table 11. DC Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 21.Bus Timing Requirements Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Table 12. AC Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 22.Power Down/Up Mode AC Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Table 13. Power Down/Up AC Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
PACKAGE MECHANICAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 23.SOH28 – 28-lead Plastic Small Outline, Battery SNAPHAT, Package Outline . . . . . . . . 28
Table 14. SOH28 – 28-lead Plastic Small Outline, battery SNAPHAT, Package Mechanical Data 28
Figure 24.SH – 4-pin SNAPHAT Housing for 48mAh Battery & Crystal, Package Outline . . . . . . . 29
Table 15. SH – 4-pin SNAPHAT Housing for 48mAh Battery & Crystal, Mechanical Data . . . . . . . 29
Figure 25.SH – 4-pin SNAPHAT Housing for 120mAh Battery & Crystal, Package Outline . . . . . . 30
Table 16. SH – 4-pin SNAPHAT Housing for 120mAh Battery & Crystal, Mechanical Data . . . . . . 30
Figure 26.SOX28 – 28-lead Plastic Small Outline, 300mils, Embedded Crystal, Package Outline. 31
Table 17. SOX28 – 28-lead Plastic Small Outline, 300mils, Embedded Crystal, Mech. Data. . . . . 31
PART NUMBERING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Table 18. Ordering Information Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Table 19. SNAPHAT Battery Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
REVISION HISTORY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Table 20. Document Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3/34
M41ST85Y, M41ST85W
SUMMARY DESCRIPTION
The M41ST85Y/W Serial TIMEKEEPER
®
/Con-
troller SRAM is a low power 512-bit, static CMOS
SRAM organized as 64 words by 8 bits. A built-in
32.768 kHz oscillator (external crystal controlled)
and 8 bytes of the SRAM (see
Table 2., page 14)
are used for the clock/calendar function and are
configured in binary coded decimal (BCD) format.
An additional 12 bytes of RAM provide status/con-
trol of Alarm, Watchdog and Square Wave func-
tions. Addresses and data are transferred serially
via a two line, bi-directional I
2
C interface. The
built-in address register is incremented automati-
cally after each WRITE or READ data byte. The
M41ST85Y/W 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
small lithium button-cell supply when a power fail-
ure occurs.
Functions available to the user include a non-vol-
atile, time-of-day clock/calendar, Alarm interrupts,
Watchdog Timer and programmable Square
Wave output. Other features include a Power-On
Reset as well as two additional debounced inputs
(RSTIN1 and RSTIN2) which can also generate an
output Reset (RST). The eight clock address loca-
tions 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 M41ST85Y/W is supplied in a 28-lead SOIC
SNAPHAT
®
package (which integrates both crys-
tal and battery in a single SNAPHAT top) or a 28-
pin, 300mil SOIC package (MX) which includes an
embedded 32kHz crystal.
The 28-pin, 330mil SOIC provides sockets with
gold plated contacts at both ends for direct con-
nection to a separate SNAPHAT housing contain-
ing 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 surface 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 SOIC and battery/crystal packages are
shipped separately in plastic anti-static tubes or in
Tape & Reel form. For the 28-lead SOIC, the bat-
tery/crystal package (e.g., SNAPHAT) part num-
ber
is
“M4TXX-BR12SH”
(see
Table
19., page 32).
Caution:
Do not place the SNAPHAT battery/crys-
tal top in conductive foam, as this will drain the lith-
ium button-cell battery.
The 300mil, embedded crystal SOIC requires only
a user-supplied battery to provide non-volatile op-
eration.
4/34
M41ST85Y, M41ST85W
Figure 3. Logic Diagram
VCC
VBAT(1)
Table 1. Signal Names
E
CON
EX
IRQ/FT/OUT
Conditioned Chip Enable Output
External Chip Enable
Interrupt/Frequency Test/Out Output
(Open Drain)
Power Fail Input
Power Fail Output
Reset Output (Open Drain)
Reset 1 Input
Reset 2 Input
Serial Clock Input
Serial Data Input/Output
Square Wave Output
Watchdog Input
Supply Voltage
Voltage Output
Ground
Battery Supply Voltage
No Connect
No Function
SCL
ECON
SDA
RST
EX
RSTIN1
RSTIN2
PFO
WDI
VOUT
PFI
M41ST85Y
M41ST85W
IRQ/FT/OUT
SQW
PFI
PFO
RST
RSTIN1
RSTIN2
SCL
SDA
SQW
WDI
V
CC
V
OUT
VSS
V
SS
AI03658
V
BAT(1)
NC
NF
Note: 1. For 28-pin, 300mil embedded crystal SOIC only.
Note: 1. For 28-pin, 300mil embedded crystal SOIC only.
Figure 4. 28-pin SOIC Connections
SQW
NC
NC
NC
NC
NC
NC
WDI
RSTIN1
RSTIN2
NC
NC
PFO
VSS
28
1
2
27
3
26
4
25
5
24
6
23
7 M41ST85Y 22
8 M41ST85W 21
9
20
10
19
11
18
12
17
13
16
14
15
AI03659
Figure 5. 28-pin, 300mil SOIC (MX)
Connections
NF
NF
NF
NF
NC
NC
NC
SQW
WDI
RSTIN1
RSTIN2
PFO
NC
VSS
28
1
2
27
3
26
4
25
5
24
6
23
7 M41ST85Y 22
8 M41ST85W 21
9
20
10
19
11
18
12
17
13
16
14
15
VCC
EX
IRQ/FT/OUT
VOUT
NC
PFI
SCL
NC
NC
RST
NC
SDA
ECON
VBAT
AI06370d
VCC
EX
IRQ/FT/OUT
VOUT
NC
NC
PFI
NC
SCL
NC
RST
NC
SDA
ECON
Note: No Function (NF) pins should be tied to V
SS
. Pins 1, 2, 3, and
4 are internally shorted together.
5/34
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