STMicroelectronics M41ST85W 3.0/3.3 v i2c combination serial rtc, nvram supervisor and microprocessor supervisor Datasheet

M41ST85W
3.0/3.3 V I2C combination serial RTC, NVRAM
supervisor and microprocessor supervisor
Features
SNAPHAT battery & crystal
■
Automatic battery switchover and WRITE
protect for:
– Internal serial RTC and
– External low power SRAM (LPSRAM)
■
400 kHz I2C serial interface
■
3.0/3.3 V operating voltage
– VCC = 2.7 to 3.6 V
■
Ultralow battery supply current of 500 nA (max)
■
RoHS compliant
– Lead-free second level interconnect
28
1
SOH28
Embedded crystal
Serial RTC features
SOX28
■
400 kHz I2C
■
44 bytes of general purpose NVRAM
■
Counters for:
– Seconds, minutes, hours, day, date, month,
and year
– Century
– Tenths/hundredths of seconds
– Clock calibration register allows
compensation for crystal variations over
temperature
■
■
Programmable alarm with repeat modes
– Functions in battery back-up mode
■
Power-down timestamp (HT bit)
■
2.5 to 5.5 V oscillator operating voltage
Power-on reset/low voltage detect
– Open drain reset output
– Reset voltage, VPFD = 2.60 V (nom)
– Two reset input pins
– Watchdog can be steered to reset output
NVRAM supervisor features
■
Non-volatizes external LPSRAM
– Automatically switches to back-up battery
and deselects (write-protects) external
LPSRAM via chip-enable gate
– Power-fail deselect (write protect) voltage,
VPFD = 2.60 V (nom)
– Switchover, VSO = 2.50 V (nom)
■
Battery monitor (battery low flag)
Microprocessor supervisor features
■
■
Other features
Programmable watchdog
– 62.5 ms to 128 s time-out period
Early power-fail warning circuit (PFI/PFO) with
1.25 V precision reference
October 2011
■
Programmable squarewave generator (1 Hz to
32 KHz)
■
–40°C to +85°C operation
■
Package options:
– 28-lead SNAPHAT® IC (SOH28) SNAPHAT
battery/crystal top to be ordered separately
– 28-lead embedded crystal SOIC (SOX28)
Doc ID 7531 Rev 11
1/43
www.st.com
1
Contents
M41ST85W
Contents
1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2
Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1
3
2-wire bus characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.1
Bus not busy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.2
Start data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.3
Stop data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.4
Data valid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.5
Acknowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2
Read mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3
Write mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.4
Data retention mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Clock operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1
Power-down time-stamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2
TIMEKEEPER® registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.3
Calibrating the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.4
Setting alarm clock registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.5
Watchdog timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.6
Square wave output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.7
Power-on reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.8
Reset inputs (RSTIN1 & RSTIN2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.9
Power-fail input/output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.10
Century bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.11
Output driver pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.12
Battery low warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.13
trec bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.14
Initial power-on defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5
DC and AC parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2/43
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M41ST85W
Contents
6
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7
Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
8
Environmental information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
9
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
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List of tables
M41ST85W
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Table 14.
Table 15.
Table 16.
Table 17.
Table 18.
Table 19.
Table 20.
Table 21.
Table 22.
4/43
Signal names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
TIMEKEEPER® register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Alarm repeat modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Square wave output frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Reset AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
trec definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Default values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
DC and AC measurement conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
DC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Power down/up AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
SOH28 – 28-lead plastic small outline, battery SNAPHAT®, package mechanical data . . 34
4-pin SNAPHAT® housing for 48 mAh battery & crystal, mechanical data. . . . . . . . . . . . . 35
4-pin SNAPHAT® housing for 120 mAh battery & crystal, mechanical data. . . . . . . . . . . . 36
SOX28 – 28-lead plastic small outline, 300 mils, embedded crystal, mechanical data . . . 37
Carrier tape dimensions for SOH28 and SOX28 packages . . . . . . . . . . . . . . . . . . . . . . . . 38
Reel dimensions for 24 mm carrier tape (SOH28 and SOX28 packages) . . . . . . . . . . . . . 39
Ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
SNAPHAT® battery/crystal table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Doc ID 7531
M41ST85W
List of figures
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
28-pin SOIC connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
28-pin, 300 mil SOIC connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Hardware hookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Serial bus data transfer sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Acknowledgement sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Write cycle timing: RTC & external SRAM control signals . . . . . . . . . . . . . . . . . . . . . . . . . 14
Slave address location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Read mode sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Alternate read mode sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Write mode sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Crystal accuracy across temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Calibration waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Alarm interrupt reset waveform. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Backup mode alarm waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
RSTIN1 & RSTIN2 timing waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
AC testing input/output waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Bus timing requirements sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Power down/up mode AC waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
SOH28 – 28-lead plastic small outline, battery SNAPHAT®, package outline . . . . . . . . . . 34
4-pin SNAPHAT® housing for 48 mAh battery & crystal, package outline . . . . . . . . . . . . . 35
4-pin SNAPHAT® housing for 120 mAh battery & crystal, package outline . . . . . . . . . . . . 36
SOX28 – 28-lead plastic small outline, 300 mils, embedded crystal, package outline . . . . 37
Carrier tape for SOH28 and SOX28 package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Reel schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Recycling symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
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Description
1
M41ST85W
Description
The M41ST85W is a combination serial real-time clock, microprocessor supervisor, and
NVRAM supervisor. It is built in a low-power CMOS SRAM process and has a 64-byte
memory space with 44 bytes of NVRAM and 20 memory-mapped RTC registers (see
Table 2 on page 20). The RTC registers are configured in binary coded decimal (BCD)
format.
The M41ST85W combines a 400 kHz I2C serial RTC with an automatic backup battery
switchover circuit for powering an external LPSRAM as well as the internal RTC. When
power begins to fail, the switchover automatically connects to the backup battery to keep the
RTC and external LPSRAM alive in the absence of system power. Access to the LPSRAM is
also cut off via a chip-enable gate function, thereby write-protecting the memory. A
programmable watchdog and power-on reset/low voltage detect function are the key
elements in the microprocessor supervisor section.
The real-time clock includes a built-in 32.768 kHz oscillator (crystal-controlled), which
provides the time base for the timekeeping and calendar functions. Eight of the 20 clock
registers provide the basic clock/calendar functions while the other 12 bytes provide
status/control for the alarm, watchdog, and squarewave functions.
RTC addresses and data are transferred serially via the two-line, bidirectional I2C interface.
The built-in address register is incremented automatically after each WRITE or READ data
byte.
The M41ST85W has a built-in power sense circuit which detects power failures and
automatically switches to the backup battery when a power failure occurs. During an outage,
the power to sustain the SRAM and clock operations is typically supplied by a small lithium
button-cell battery as is the case when using the SNAPHAT® package option.
Functions available to the user include a non-volatile, time-of-day clock/calendar, alarm
interrupts, watchdog timer, and programmable squarewave generator. Other features
include a power-on reset as well as two additional debounce reset inputs (RSTIN1 and
RSTIN2) which can also generate an output reset (RST).
The eight registers for basic clock/calendar functions 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 M41ST85W is offered in two 28-lead SOIC packages. The 300 mil SOH28 SNAPHAT®
IC package mates with ST’s SNAPHAT battery/crystal top (ordered separately). SNAPHAT
battery options include 48 mAh and 120 mAh. ST’s 300 mil SOX28 embedded crystal IC
includes the 32 KHz crystal and is perfect for applications where a low profile is a must.
The SOH28 SNAPHAT SOIC includes sockets with gold plated contacts at both ends for
direct connection to the SNAPHAT top. The SNAPHAT battery/crystal top is inserted atop
the IC package after the completion of the surface mount assembly process which avoids
potential battery and crystal damage due to the high temperatures required for device
surface-mounting. The unique design allows the battery to be replaced, thus extending the
life of the RTC and NVRAM indefinitely.
The SNAPHAT top is keyed to prevent reverse insertion. The SNAPHAT IC and SNAPHAT
tops are shipped separately. The ICs are available in plastic anti-static tubes or in tape &
reel form. The SNAPHAT tops are shipped in plastic anti-static tubes. The part numbers are
6/43
Doc ID 7531 Rev 11
M41ST85W
Description
M4T28-BR12SH1 (48 mAh) and M4T32-BR12SH1 (120 mAh). For the extended
temperature requirement, the 120 mAh M4T32-BR12SH6 is available. For more information,
see Table 21 on page 40.
Caution:
Do not place the SNAPHAT® battery/crystal top in conductive foam, as this will drain the
lithium button-cell battery.
The 300 mil SOX embedded crystal SOIC typically requires a user-supplied battery for nonvolatile operation. Capacitor backup can also be implemented with this package.
Figure 1.
Logic diagram
VCC
VBAT(1)
SCL
ECON
SDA
RST
EX
IRQ/FT/OUT
RSTIN1
M41ST85W
SQW
RSTIN2
PFO
WDI
VOUT
PFI
VSS
AI03658
1. For 28-pin, 300 mil embedded crystal SOIC only.
Doc ID 7531 Rev 11
7/43
Description
M41ST85W
Table 1.
Signal names
ECON
Conditioned chip enable output
EX
External chip enable
IRQ/FT/OUT
Interrupt/frequency test/out output (open drain)
PFI
Power fail input
PFO
Power fail output
RST
Reset output (open drain)
RSTIN1
Reset 1 Input
RSTIN2
Reset 2 Input
SCL
Serial clock input
SDA
Serial data input/output
SQW
Square wave output
WDI
Watchdog input
VCC
Supply voltage
VOUT
Voltage output
VSS
Ground
VBAT
(1)
Battery supply voltage
NC
No connect
NF
No function
1. For 28-pin, 300 mil embedded crystal SOIC only.
Figure 2.
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
22
M41ST85W
8
21
9
20
10
19
11
18
12
17
13
16
14
15
AI03659
8/43
Doc ID 7531 Rev 11
VCC
EX
IRQ/FT/OUT
VOUT
NC
NC
PFI
NC
SCL
NC
RST
NC
SDA
ECON
M41ST85W
Description
Figure 3.
28-pin, 300 mil SOIC 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
22
M41ST85W
8
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
Note:
No function (NF) pins should be tied to VSS. Pins 1, 2, 3, and 4 are internally
shorted together.
Doc ID 7531 Rev 11
9/43
Description
Figure 4.
M41ST85W
Block diagram
REAL TIME CLOCK
CALENDAR
SDA
44 BYTES
USER RAM
I2C
INTERFACE
RTC w/ALARM
& CALIBRATION
SCL
(2)
Crystal
WATCHDOG
32KHz
OSCILLATOR
SQUARE WAVE
WDI
VCC
AFE
WDS
IRQ/FT/OUT(1)
SQW
VOUT
VBAT
VBL= 2.5V
COMPARE
VSO = 2.5V
COMPARE
VPFD = 2.65V
COMPARE
BL
POR
RST(1)
RSTIN1
RSTIN2
ECON
EX
PFI
COMPARE
PFO
1.25V
(Internal)
AI03932
1. Open drain output.
2. Crystal integrated into SOIC package for MX package option.
10/43
Doc ID 7531 Rev 11
M41ST85W
Figure 5.
Description
Hardware hookup
M41ST85W
Regulator
Unregulated
Voltage
VIN
VCC
VCC
VOUT
VCC
ECON
E
EX
LPSRAM
From MCU
SCL
R1
SDA
WDI
Pushbutton
Reset
RSTIN1
RST
RSTIN2
SQW
To RST
To LED Display
PFO
To NMI
(1) IRQ/FT/OUT
VBAT
To INT
PFI
R2
VSS
AI03660
1. Required for embedded crystal (MX) package only.
Doc ID 7531 Rev 11
11/43
Operating modes
2
M41ST85W
Operating modes
The M41ST85W 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 64 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.
Control register
10. Watchdog register
11 - 16. Alarm registers
17 - 19. Reserved
20. Square wave register
21 - 64. User RAM
The M41ST85W 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. When VCC falls
below VSO, the device automatically switches over to the battery and powers down into an
ultralow current mode of operation to conserve battery life. As system power returns and
VCC rises above VSO, the battery is disconnected, and the power supply is switched to
external VCC.
Write protection continues until VCC reaches VPFD(min) plus trec (min).
For more information on battery storage life refer to application note AN1012.
2.1
2-wire bus characteristics
The bus is intended for communication between different ICs. It consists of two lines: a bidirectional 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.
The following protocol has been defined:
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●
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.
Doc ID 7531 Rev 11
M41ST85W
Operating modes
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.
2.1.4
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.”
2.1.5
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
case the transmitter must leave the data line high to enable the master to generate the
STOP condition.
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Operating modes
Figure 6.
M41ST85W
Serial bus data transfer sequence
DATA LINE
STABLE
DATA VALID
CLOCK
DATA
START
CONDITION
CHANGE OF
DATA ALLOWED
STOP
CONDITION
AI00587
Figure 7.
Acknowledgement sequence
CLOCK PULSE FOR
ACKNOWLEDGEMENT
START
SCL FROM
MASTER
DATA OUTPUT
BY TRANSMITTER
1
2
8
MSB
9
LSB
DATA OUTPUT
BY RECEIVER
AI00601
Figure 8.
Write cycle timing: RTC & external SRAM control signals
EX
tEXPD
tEXPD
ECON
AI03663
14/43
Doc ID 7531 Rev 11
M41ST85W
2.2
Operating modes
Read mode
In this mode the master reads the M41ST85W slave after setting the slave address (see
Figure 9). 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 (see Figure 10 on page 16). The address pointer is
only incremented on reception of an acknowledge clock. The M41ST85W 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 either due to a stop condition or when
the pointer increments to a non-clock or RAM address.
This is true both in READ mode and WRITE mode.
An alternate READ mode may also be implemented whereby the master reads the
M41ST85W 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 11 on page 16).
Slave address location
R/W
SLAVE ADDRESS
START
1
A
LSB
Figure 9.
MSB
Note:
1
0
1
0
0
0
AI00602
Doc ID 7531 Rev 11
15/43
Operating modes
M41ST85W
SLAVE
ADDRESS
DATA n+1
ACK
DATA n
ACK
S
ACK
BUS ACTIVITY:
R/W
START
WORD
ADDRESS (An)
ACK
S
R/W
SDA LINE
ACK
BUS ACTIVITY:
MASTER
START
Figure 10. Read mode sequence
STOP
SLAVE
ADDRESS
DATA n+X
P
NO ACK
AI00899
STOP
R/W
SLAVE
ADDRESS
16/43
DATA n+X
P
NO ACK
BUS ACTIVITY:
DATA n+1
ACK
DATA n
ACK
S
ACK
SDA LINE
ACK
BUS ACTIVITY:
MASTER
START
Figure 11. Alternate read mode sequence
AI00895
Doc ID 7531 Rev 11
M41ST85W
2.3
Operating modes
Write mode
In this mode the master transmitter transmits to the M41ST85W slave receiver. Bus protocol
is shown in Figure 12. 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
memory location within the RAM on the reception of an acknowledge clock. The M41ST85W
slave receiver will send an acknowledge clock to the master transmitter after it has received
the slave address and again after it has received the word address and each data byte.
STOP
SLAVE
ADDRESS
2.4
DATA n+X
P
ACK
DATA n+1
ACK
BUS ACTIVITY:
DATA n
ACK
WORD
ADDRESS (An)
ACK
S
R/W
SDA LINE
ACK
BUS ACTIVITY:
MASTER
START
Figure 12. Write mode sequence
AI00591
Data retention mode
With valid VCC applied, the M41ST85W can be accessed as described above with READ or
WRITE cycles. Should the supply voltage decay, the M41ST85W will automatically deselect,
write protecting itself (and any external SRAM) when VCC falls between VPFD(max) and
VPFD(min). This is accomplished by internally inhibiting access to the clock registers. At this
time, the reset pin (RST) is driven active and will remain active until VCC returns to nominal
levels. External RAM access is inhibited in a similar manner by forcing ECON to a high level.
This level is within 0.2 volts of the VBAT. ECON will remain at this level as long as VCC
remains at an out-of-tolerance condition. When VCC falls below the battery backup
switchover voltage (VSO), power input is switched from the VCC pin to the SNAPHAT®
battery, and the clock registers and external SRAM are maintained from the attached
battery supply.
All outputs become high impedance. The VOUT pin is capable of supplying 100 µA of current
to the attached memory with less than 0.3 volts drop under this condition. On power-up,
when VCC returns to a nominal value, write protection continues for trec by inhibiting ECON.
The RST signal also remains active during this time (see Figure 20 on page 33).
Note:
Most low power SRAMs on the market today can be used with the M41ST85W RTC
SUPERVISOR. There are, however some criteria which should be used in making the final
choice of an SRAM to use. The SRAM must be designed in a way where the chip enable
input disables all other inputs to the SRAM. This allows inputs to the M41ST85W and
SRAMs to be “Don’t Care” once VCC falls below VPFD(min). The SRAM should also
guarantee data retention down to VCC = 2.0 volts. The chip enable access time must be
sufficient to meet the system needs with the chip enable output propagation delays
included. If the SRAM includes a second chip enable pin (E2), this pin should be tied to
VOUT.
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Operating modes
M41ST85W
If data retention lifetime is a critical parameter for the system, it is important to review the
data retention current specifications for the particular SRAMs being evaluated. Most SRAMs
specify a data retention current at 3.0 volts. Manufacturers generally specify a typical
condition for room temperature along with a worst case condition (generally at elevated
temperatures). The system level requirements will determine the choice of which value to
use. The data retention current value of the SRAMs can then be added to the IBAT value of
the M41ST85W to determine the total current requirements for data retention. The available
battery capacity for the SNAPHAT® top of your choice can then be divided by this current to
determine the amount of data retention available (see Table 21 on page 40).
For a further more detailed review of lifetime calculations, please see application note
AN1012.
18/43
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M41ST85W
3
Clock operation
Clock operation
The eight byte clock register (see Table 2 on page 20) 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:
A WRITE to any clock register will result in the tenths/hundredths of seconds being reset to
“00,” and 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 control 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. The
control register (address location 08h) may be accessed independently. 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.
3.1
Power-down time-stamp
When a power failure occurs, the halt update bit (HT) will automatically be set to a '1.' This
will prevent the clock from updating the TIMEKEEPER® 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 TIMEKEEPER registers with the current time. For more information, see
application note AN1572.
3.2
TIMEKEEPER® registers
The M41ST85W offers 20 internal registers which contain clock, alarm, watchdog, flag,
square wave and control data. These registers are memory locations which contain external
(user accessible) and internal copies of the data (usually referred to as BiPORT™
TIMEKEEPER 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 a non-clock or RAM address.
TIMEKEEPER and alarm registers store data in BCD. control, watchdog and square wave
registers store data in binary format.
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Clock operation
M41ST85W
TIMEKEEPER® register map
Table 2.
Data
Function/range
Address
D7
D6
00h
D5
D4
D3
D2
0.1 seconds
D1
BCD format
D0
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
Hours (24-hour format)
Century/hours
0-1/00-23
04h
TR
0
Day
01-7
05h
0
0
Date: day of month
Date
01-31
06h
0
0
Month
Month
01-12
Year
Year
00-99
07h
10 hours
0
0
0
10 date
0
Day of week
10M
10 years
08h
OUT
FT
S
09h
WDS
BMB4
BMB3
BMB2
0Ah
AFE
SQWE
ABE
Al 10M
0Bh
RPT4
RPT5
0Ch
RPT3
HT
0Dh
RPT2
0Eh
RPT1
0Fh
WDF
AF
0
BL
0
0
0
0
Flags
10h
0
0
0
0
0
0
0
0
Reserved
11h
0
0
0
0
0
0
0
0
Reserved
12h
0
0
0
0
0
0
0
0
Reserved
13h
RS3
RS2
RS1
RS0
0
0
0
0
SQW
Keys:
20/43
Calibration
BMB1
BMB0
Control
RB1
RB0
Watchdog
Alarm month
Al month
01-12
AI 10 date
Alarm date
Al date
01-31
AI 10 hour
Alarm hour
Al hour
00-23
Alarm 10 minutes
Alarm minutes
Al min
00-59
Alarm 10 seconds
Alarm seconds
Al sec
00-59
S = Sign bit
RB0-RB1 = Watchdog resolution bits
FT = Frequency test bit
WDS = Watchdog steering bit
ST = Stop bit
ABE = Alarm in battery backup mode enable bit
0 = Must be set to zero
RPT1-RPT5 = Alarm repeat mode bits
BL = Battery low flag (read only)
WDF = Watchdog flag (read only)
BMB0-BMB4 = Watchdog multiplier bits
AF = Alarm flag (read only)
CEB = Century enable bit
SQWE = Square wave enable
CB = Century bit
RS0-RS3 = SQW frequency
OUT = Output level
HT = Halt update bit
AFE = Alarm flag enable flag
TR = trec bit
Doc ID 7531 Rev 11
M41ST85W
3.3
Clock operation
Calibrating the clock
The M41ST85W 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 +/–1.53 minutes per month. 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 (see Figure 13 on page 22).
Therefore, the M41ST85W 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 14 on page 22. 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 control 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 control 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. Assuming that the oscillator is
running at exactly 32,768 Hz, 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 M41ST85W 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 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 watchdog steering bit (WDS, D7 of 09h) is '1' or the watchdog register (09h = 0) is
reset.
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.
The IRQ/FT/OUT pin is an open drain output which requires a pull-up resistor to VCC for
proper operation. A 500 to 10 k resistor is recommended in order to control the rise time.
The FT bit is cleared on power-down.
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Clock operation
M41ST85W
Figure 13. Crystal accuracy across temperature
Frequency (ppm)
20
0
–20
–40
–60
ΔF = K x (T – T )2
O
F
–80
2
2
K = –0.036 ppm/°C ± 0.006 ppm/°C
–100
TO = 25°C ± 5°C
–120
–140
–160
–40
–30
–20
–10
0
10
20
30
40
50
60
70
80
Temperature °C
AI07888
Figure 14. Calibration waveform
NORMAL
POSITIVE
CALIBRATION
NEGATIVE
CALIBRATION
AI00594B
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M41ST85W
3.4
Clock operation
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
M41ST85W is in the battery backup to serve as a system wake-up call.
Bits RPT5–RPT1 put the alarm in the repeat mode of operation. Table 3 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.
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, the
alarm condition activates the IRQ/FT/OUT pin as shown in Figure 15. To disable alarm,
write '0' to the alarm date register and to RPT5–RPT1.
Note:
If the address pointer is allowed to increment to the flag 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 output is cleared by a READ to the flags register. 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 pin can also be activated in the battery backup mode. The IRQ/FT/OUT
will go low if an alarm occurs and both ABE (alarm in battery backup mode enable) and AFE
are set. The ABE and AFE bits are reset during power-up, therefore an alarm generated
during power-up will only set AF. The user can read the flag register at system boot-up to
determine if an alarm was generated while the M41ST85W was in the deselect mode during
power-up. Figure 16 on page 24 illustrates the backup mode alarm timing.
Figure 15. Alarm interrupt reset waveform
0Eh
0Fh
10h
ACTIVE FLAG
HIGH-Z
IRQ/FT/OUT
AI03664
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
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Clock operation
M41ST85W
Figure 16. Backup mode alarm waveform
VCC
VPFD
VSO
trec
ABE, AFE Bits in Interrupt Register
AF bit in Flags Register
IRQ/FT/OUT
HIGH-Z
HIGH-Z
AI03920
3.5
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
register, address 09h. Bits BMB4-BMB0 store a binary multiplier and the two lower order bits
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).
Note:
The accuracy of the timer is within ± the selected resolution.
If the processor does not reset the timer within the specified period, the M41ST85W sets the
WDF (watchdog flag) and generates a watchdog interrupt or a microprocessor reset.
The most significant bit of the watchdog register is the watchdog steering bit (WDS). When
set to a '0,' the watchdog will activate the IRQ/FT/OUT pin when timed-out. When WDS is
set to a '1,' the watchdog will output a negative pulse on the RST pin for trec. The watchdog
register, FT, AFE, ABE and SQWE bits will reset to a '0' at the end of a watchdog time-out
when the WDS bit is set to a '1.'
The watchdog timer can be reset by two methods: 1) a transition (high-to-low or low-to-high)
can be applied to the watchdog input pin (WDI) or 2) the microprocessor can perform a
WRITE of the watchdog register. The time-out period then starts over.
Note:
The WDI pin should be tied to VSS if not used.
In order to perform a software reset of the watchdog timer, the original time-out period can
be written into the watchdog register, effectively restarting the count-down cycle.
Should the watchdog timer time-out, and the WDS bit is programmed to output an interrupt,
a value of 00h needs to be written to the watchdog register in order to clear the IRQ/FT/OUT
24/43
Doc ID 7531 Rev 11
M41ST85W
Clock operation
pin. This will also disable 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 to output to the IRQ/FT/OUT pin and the frequency
test function is activated, the watchdog function prevails and the frequency test function is
denied.
3.6
Square wave output
The M41ST85W 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 Table 4. Once the selection of the SQW frequency has been
completed, the SQW pin can be turned on and off under software control with the square
wave enable bit (SQWE) located in register 0Ah.
Table 4.
Square wave output frequency
Square wave bits
3.7
Square wave
RS3
RS2
RS1
RS0
Frequency
Units
0
0
0
0
None
–
0
0
0
1
32.768
kHz
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
0
1
1
0
512
Hz
0
1
1
1
256
Hz
1
0
0
0
128
Hz
1
0
0
1
64
Hz
1
0
1
0
32
Hz
1
0
1
1
16
Hz
1
1
0
0
8
Hz
1
1
0
1
4
Hz
1
1
1
0
2
Hz
1
1
1
1
1
Hz
Power-on reset
The M41ST85W continuously monitors VCC. When VCC falls to the power fail detect trip
point, the RST pulls low (open drain) and remains low on power-up for trec after VCC passes
VPFD(max). The RST pin is an open drain output and an appropriate pull-up resistor should
be chosen to control rise time.
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Clock operation
3.8
M41ST85W
Reset inputs (RSTIN1 & RSTIN2)
The M41ST85W provides two independent inputs which can generate an output reset. The
duration and function of these resets is identical to a reset generated by a power cycle.
Table 5 and Figure 17 illustrate the AC reset characteristics of this function. Pulses shorter
than tRLRH1 and tRLRH2 will not generate a reset condition. RSTIN1 and RSTIN2 are each
internally pulled up to VCC through a 100 kΩ resistor.
Figure 17. RSTIN1 & RSTIN2 timing waveforms
RSTIN1
tRLRH1
RSTIN2
tRLRH2
RST
(1)
tR1HRH
tR2HRH
AI03665
Note:
With pull-up resistor
Table 5.
Reset AC characteristics
Symbol
tRLRH1(2)
tRLRH2(3)
tR1HRH(4)
tR2HRH(4)
Parameter(1)
Min
Max
Unit
RSTIN1 low to RSTIN1 high
200
ns
RSTIN2 low to RSTIN2 high
100
RSTIN1 high to RST high
40
200
ms
RSTIN2 high to RST high
40
200
ms
ms
1. Valid for ambient operating temperature: TA = –40 to 85°C; VCC = 2.7 to 3.6 V (except where noted).
2. Pulse width less than 50 ns will result in no RESET (for noise immunity).
3. Pulse width less than 20 ms will result in no RESET (for noise immunity).
4. Programmable (see Table 6 on page 28).
3.9
Power-fail input/output
The power-fail input (PFI) is compared to an internal reference voltage (1.25 V). If PFI is less
than the power-fail threshold (VPFI), the power-fail output (PFO) will go low. This function is
intended for use as an undervoltage detector to signal a failing power supply. Typically PFI is
connected through an external voltage divider (see Figure 5 on page 11) to either the
unregulated DC input (if it is available) or the regulated output of the VCC regulator. The
voltage divider can be set up such that the voltage at PFI falls below VPFI several
milliseconds before the regulated VCC input to the M41ST85W or the microprocessor drops
below the minimum operating voltage.
During battery backup, the power-fail comparator turns off and PFO goes (or remains) low.
This occurs after VCC drops below VPFD(min). When power returns, PFO is forced high,
irrespective of VPFI for the write protect time (trec), which is the time from VPFD(max) until the
inputs are recognized. At the end of this time, the power-fail comparator is enabled and PFO
26/43
Doc ID 7531 Rev 11
M41ST85W
Clock operation
follows PFI. If the comparator is unused, PFI should be connected to VSS and PFO left
unconnected.
3.10
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.
3.11
Output driver pin
When the FT bit, AFE bit and watchdog register are not set, the IRQ/FT/OUT pin becomes
an output driver that reflects the contents of D7 of the control register. In other words, when
D7 (OUT bit) and D6 (FT bit) of address location 08h are a '0,' then the IRQ/FT/OUT pin will
be driven low.
Note:
The IRQ/FT/OUT pin is an open drain which requires an external pull-up resistor.
3.12
Battery low warning
The M41ST85W 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 in the SRAM.
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 backup mode, the battery should be replaced. The SNAPHAT® top may be replaced
while VCC is applied to the device.
Note:
This will cause the clock to lose time during the interval the SNAPHAT battery/crystal top is
disconnected.
The M41ST85W 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.
Doc ID 7531 Rev 11
27/43
Clock operation
3.13
M41ST85W
trec bit
Bit D7 of clock register 04h contains the trec bit (TR). trec refers to the automatic
continuation of the deselect time after VCC reaches VPFD. This allows for a voltage settling
time before WRITEs may again be performed to the device after a power-down condition.
The trec bit will allow the user to set the length of this deselect time as defined by Table 6.
3.14
Initial power-on defaults
Upon initial application of power to the device, the following register bits are set to a '0' state:
watchdog register, FT, AFE, ABE, SQWE, and TR. The following bits are set to a '1' state:
ST, OUT, and HT (see Table 7).
Table 6.
trec definitions
trec bit (TR)
STOP bit (ST)
0
0
trec time
Units
Min
Max
96
98
(1)
ms
0
1
40
200
ms
1
X
50
2000
µs
1. Default setting
Table 7.
Default values
Condition
Initial power-up(2)
Subsequent power-up
(with battery backup)(3)
TR
ST
HT
Out
FT
AFE
ABE
SQWE
Watchdog
register(1)
0
1
1
1
0
0
0
0
0
UC
UC
1
UC
0
0
0
0
0
1. WDS, BMB0-BMB4, RB0, RB1.
2. State of other control bits undefined.
3. UC = Unchanged
28/43
Doc ID 7531 Rev 11
M41ST85W
4
Maximum ratings
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. Refer also to the STMicroelectronics SURE
Program and other relevant quality documents.
Table 8.
Absolute maximum ratings
Symbol
TSTG
TSLD
Parameter
Storage temperature (VCC off, oscillator
off)
Lead solder temperature for 10 seconds
Value
Unit
SNAPHAT®
–40 to 85
°C
SOIC
–55 to 150
°C
SOH28(1)
260
°C
SOX28(2)
240
°C
–0.3 to VCC+0.3
V
VIO
Input or output voltage
VCC
Supply voltage
–0.3 to 4.6
V
IO
Output current
20
mA
PD
Power dissipation
1
W
1. For SOH28 package, lead-free (pb-free) lead finish: reflow at peak temperature of 260°C (the time above
255°C must not exceed 30 seconds).
2. The SOX28 package has lead-free (pb-free) lead finish, but cannot be exposed to peak reflow temperature
in excess of 240°C. Reflow at peak temperature of 240°C (the time above 235°C must not exceed 20
seconds).
Caution:
Negative undershoots below –0.3 V are not allowed on any pin while in the battery backup
mode.
Caution:
Do NOT wave solder SOIC to avoid damaging SNAPHAT sockets.
Doc ID 7531 Rev 11
29/43
DC and AC parameters
5
M41ST85W
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 9.
DC and AC measurement conditions
Parameter
Note:
M41ST85W
VCC supply voltage
2.7 to 3.6 V
Ambient operating temperature
–40 to 85°C
Load capacitance (CL)
50 pF
Input rise and fall times
≤ 50 ns
Input pulse voltages
0.2 to 0.8VCC
Input and output timing ref. voltages
0.3 to 0.7VCC
Output High Z is defined as the point where data is no longer driven.
Figure 18. AC testing input/output waveforms
0.8VCC
0.7VCC
0.3VCC
0.2VCC
AI02568
Table 10.
Capacitance
Parameter(1)(2)
Symbol
CIN
COUT(3)
tLP
Min
Max
Unit
Input capacitance
7
pF
Output capacitance
10
pF
Low-pass filter input time constant (SDA and SCL)
50
ns
1. Effective capacitance measured with power supply at 5 V. Sampled only, not 100% tested.
2. At 25°C, f = 1 MHz.
3. Outputs are deselected.
30/43
Doc ID 7531 Rev 11
M41ST85W
Table 11.
DC and AC parameters
DC characteristics
Sym
Parameter
M41ST85W
Test condition(1)
Unit
Min
IBAT(2)
ICC1
ICC2
ILI(3)
ILO(4)
IOUT1(5)
IOUT2
Battery current OSC ON
Battery current OSC OFF
Supply current
Supply current (standby)
Input leakage current
TA = 25°C, VCC = 0 V, VBAT = 3 V
Typ
Max
400
500
nA
50
nA
f = 400 kHz
0.75
mA
SCL, SDA = VCC – 0.3 V
or VSS + 0.3 V
0.50
mA
0V ≤ VIN ≤ VCC
±1
µA
25
nA
Input leakage current (PFI)
–25
2
0V ≤ VIN ≤ VCC
±1
µA
VOUT current (active)
VOUT1 > VCC – 0.3 V
100
mA
VOUT current (battery backup)
VOUT2 > VBAT – 0.3 V
100
µA
Output leakage current
VIH
Input high voltage
0.7VCC
VCC + 0.3
V
VIL
Input low voltage
–0.3
0.3VCC
V
2.5
3.5(6)
V
VBAT
VOH
VOHB(8)
VOL
VPFD
VPFI
VSO
Battery voltage
voltage(7)
IOH = –1.0 mA
Pull-up supply voltage (open drain)
RST, IRQ/FT/OUT
Output high
VOH (battery backup)
IOUT2 = –1.0 µA
3.0
2.4
2.5
V
2.9
3.6
V
3.5
V
Output low voltage
IOL = 3.0 mA
0.4
V
Output low voltage (open drain)(9)
IOL = 10 mA
0.4
V
V
Power fail deselect
PFI input threshold
PFI hysteresis
VCC = 3 V(W)
PFI rising
Battery backup switchover
2.55
2.60
2.70
1.225
1.250
1.275
V
20
70
mV
2.5
V
1. Valid for ambient operating temperature: TA = –40 to 85°C; VCC = 2.7 to 3.6 V (except where noted).
2. Measured with VOUT and ECON open.
3. RSTIN1 and RSTIN2 internally pulled-up to VCC through 100 kΩ resistor. WDI internally pulled-down to VSS through
100 kΩ resistor.
4. Outputs deselected.
5. External SRAM must match RTC supervisor chip VCC specification.
6. For rechargeable backup, VBAT (max) may be considered VCC.
7. For PFO and SQW pins (CMOS).
8. Conditioned output (ECON) can only sustain CMOS leakage current in the battery backup mode. Higher leakage currents
will reduce battery life.
9. For IRQ/FT/OUT, RST pins (open drain): if pulled-up to supply other than VCC, this supply must be equal to, or less than
3.0 V when VCC = 0 V (during battery backup mode).
Doc ID 7531 Rev 11
31/43
DC and AC parameters
M41ST85W
Figure 19. Bus timing requirements sequence
SDA
tBUF
tHD:STA
tHD:STA
tR
tF
SCL
tHIGH
P
S
tLOW
tSU:DAT
tHD:DAT
tSU:STA
SR
tSU:STO
P
AI00589
Table 12.
AC characteristics
Parameter(1)
Symbol
fSCL
SCL clock frequency
tBUF
Time the bus must be free before a new transmission can start
tEXPD
EX to ECON propagation delay
tF
tHD:DAT(2)
Min
Max
Unit
0
400
kHz
1.3
SDA and SCL fall time
15
ns
300
ns
0
µs
START condition hold time (after this period the first clock pulse is generated)
600
ns
tHIGH
Clock high period
600
ns
tLOW
Clock low period
1.3
tHD:STA
tR
Data hold time
µs
SDA and SCL rise time
µs
300
ns
tSU:DAT
Data setup time
100
ns
tSU:STA
START condition setup time (only relevant for a repeated start condition)
600
ns
tSU:STO
STOP condition setup time
600
ns
1. Valid for ambient operating temperature: TA = –40 to 85°C; VCC = 2.7 to 3.6 V (except where otherwise noted).
2. Transmitter must internally provide a hold time to bridge the undefined region (300 ns max) of the falling edge of SCL.
32/43
Doc ID 7531 Rev 11
M41ST85W
DC and AC parameters
Figure 20. Power down/up mode AC waveforms
VCC
VPFD (max)
VPFD (min)
VSO
tF
tR
tFB
tRB
tDR
tPD
trec
PFO
INPUTS
DON'T CARE
RECOGNIZED
RECOGNIZED
RST
HIGH-Z
OUTPUTS
VALID
VALID
(PER CONTROL INPUT)
(PER CONTROL INPUT)
ECON
AI03661
Table 13.
Symbol
Power down/up AC characteristics
Parameter(1)
Min
Typ
Max
Unit
tF(2)
VPFD(max) to VPFD(min) VCC fall time
300
µs
tFB(3)
VPFD(min) to VSS VCC fall time
10
µs
tPD
EX at VIH before power down
0
µs
tPFD
PFI to PFO propagation delay
15
25
µs
tR
VPFD(min) to VPFD(max) VCC rise time
10
µs
tRB
VSS to VPFD(min) VCC rise time
1
µs
Power-up deselect time
40
trec
(4)
200
ms
1. Valid for ambient operating temperature: TA = –40 to 85°C; VCC = 2.7 to 3.6 V (except where otherwise noted).
2. VPFD(max) to VPFD(min) fall time of less than tF may result in deselection/write protection not occurring until
200 µs after VCC passes VPFD(min).
3. VPFD(min) to VSS fall time of less than tFB may cause corruption of RAM data.
4. Programmable (see Table 6 on page 28)
Doc ID 7531 Rev 11
33/43
Package mechanical data
6
M41ST85W
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 21. SOH28 – 28-lead plastic small outline, battery SNAPHAT®, package outline
A2
A
C
B
eB
e
CP
D
N
E
H
A1
α
L
1
SOH-A
Note:
Drawing is not to scale.
Table 14.
SOH28 – 28-lead plastic small outline, battery SNAPHAT®, package mechanical data
millimeters
inches
Symbol
Typ
Min
A
Typ
Min
3.05
Max
0.120
A1
0.05
0.36
0.002
0.014
A2
2.34
2.69
0.092
0.106
B
0.36
0.51
0.014
0.020
C
0.15
0.32
0.006
0.012
D
17.71
18.49
0.697
0.728
E
8.23
8.89
0.324
0.350
–
–
–
–
eB
3.20
3.61
0.126
0.142
H
11.51
12.70
0.453
0.500
L
0.41
1.27
0.016
0.050
a
0°
8°
0°
8°
N
28
e
CP
34/43
Max
1.27
0.050
28
0.10
Doc ID 7531 Rev 11
0.004
M41ST85W
Package mechanical data
Figure 22. 4-pin SNAPHAT® housing for 48 mAh battery & crystal, package outline
A1
A2
A3
A
eA
B
L
eB
D
E
SHTK-A
Note:
Drawing is not to scale.
Table 15.
4-pin SNAPHAT® housing for 48 mAh battery & crystal, mechanical data
millimeters
inches
Symbol
Typ
Min
A
Max
Typ
Min
9.78
Max
0.3850
A1
6.73
7.24
0.2650
0.2850
A2
6.48
6.99
0.2551
0.2752
A3
0.38
0.0150
B
0.46
0.56
0.0181
0.0220
D
21.21
21.84
0.8350
0.8598
E
14.22
14.99
0.5598
0.5902
eA
15.55
15.95
0.6122
0.6280
eB
3.20
3.61
0.1260
0.1421
L
2.03
2.29
0.0799
0.0902
Doc ID 7531 Rev 11
35/43
Package mechanical data
M41ST85W
Figure 23. 4-pin SNAPHAT® housing for 120 mAh battery & crystal, package outline
A1
A2
A3
A
eA
B
L
eB
D
E
SHTK-A
Note:
Drawing is not to scale.
Table 16.
4-pin SNAPHAT® housing for 120 mAh battery & crystal, mechanical data
millimeters
inches
Symbol
Typ
Min
A
Typ
Min
10.54
Max
0.415
A1
8.00
8.51
0.315
0.335
A2
7.24
8.00
0.285
0.315
A3
36/43
Max
0.38
0.015
B
0.46
0.56
0.018
0.022
D
21.21
21.84
0.835
0.860
E
17.27
18.03
0.680
0.710
eA
15.55
15.95
0.612
0.628
eB
3.20
3.61
0.126
0.142
L
2.03
2.29
0.080
0.090
Doc ID 7531 Rev 11
M41ST85W
Package mechanical data
Figure 24. SOX28 – 28-lead plastic small outline, 300 mils, embedded crystal, package outline
D
14
h x 45°
1
C
E
15
H
28
A2
A
B
ddd
A1
e
A1
α
L
SO-E
Note:
Drawing is not to scale.
Table 17.
SOX28 – 28-lead plastic small outline, 300 mils, embedded crystal, mechanical data
millimeters
inches
Symbol
Typ
Min
Max
A
2.44
A1
Min
Max
2.69
0.096
0.106
0.15
0.31
0.006
0.012
A2
2.29
2.39
0.090
0.094
B
0.41
0.51
0.016
0.020
C
0.20
0.31
0.008
0.012
D
17.91
18.01
0.705
0.709
ddd
Typ
0.10
E
7.57
7.67
–
–
H
10.16
L
0.004
0.298
0.302
–
–
10.52
0.400
0.414
0.51
0.81
0.020
0.032
a
0°
8°
0°
8°
N
28
e
1.27
0.050
28
Doc ID 7531 Rev 11
37/43
Package mechanical data
M41ST85W
Figure 25. Carrier tape for SOH28 and SOX28 package
P0
E
P2
D
T
A0
F
TOP COVER
TAPE
W
B0
P1
CENTER LINES
OF CAVITY
K0
USER DIRECTION OF FEED
AM03073v1
Table 18.
Carrier tape dimensions for SOH28 and SOX28 packages
Package
W
D
SOH28
24.00
±0.30
1.50
+0.10/
–0.00
SOX28
24.00
±0.30
1.50
+0.10/
–0.00
38/43
A0
B0
K0
P1
T
Unit
Bulk
Qty
1.75
4.00
2.00 11.50
±0.10 ±0.10 ±0.10 ±0.10
12.90
±0.10
18.70
±0.10
3.20
±0.10
16.00
±0.10
0.30
±0.05
mm
936
1.75
4.00
2.00 11.50
±0.10 ±0.10 ±0.10 ±0.10
12.70
±0.10
18.20
±0.10
3.20
±0.10
16.00
±0.10
0.30
±0.05
mm 1000
E
P0
P2
F
Doc ID 7531 Rev 11
M41ST85W
Package mechanical data
Figure 26. Reel schematic
T
40mm min.
Access hole
At slot location
B
D
C
N
A
G measured
Tape slot
In core for
Full radius
At hub
Tape start
2.5mm min.width
AM04928v1
Table 19.
Reel dimensions for 24 mm carrier tape (SOH28 and SOX28 packages)
Carrier tape
24 mm
(SOH28, SOX28)
Note:
A
B
(max)
(min)
330 mm
(13-inch)
1.5 mm
C
13 mm
± 0.2 mm
D
N
(min)
(min)
20.2 mm
60 mm
G
24.4 mm
+ 2/–0 mm
T
(max)
30.4 mm
The dimensions given in Table 19 incorporate tolerances that cover all variations on critical
parameters.
Doc ID 7531 Rev 11
39/43
Part numbering
7
M41ST85W
Part numbering
Table 20.
Ordering information scheme
Example:
M41ST
85W
MH
6
E
Device type
M41ST
Supply voltage and write protect voltage
85W = VCC = 2.7 to 3.6 V; 2.55V ≤ VPFD ≤ 2.70 V
Package
MH(1) = SOH28
MX(2) = SOX28
Temperature range
6 = –40 to 85°C
Shipping method
For SOH28:
E = ECOPACK® package, tubes(3)
F = ECOPACK® package, tape & reel
For SOX28:
Blank = ECOPACK® package, tubes(3)
TR = ECOPACK® package, tape & reel
1. The 28-pin SOIC package (SOH28) requires the SNAPHAT® battery/crystal package which is ordered
separately under the part number “M4TXX-BR12SHx” in plastic tube (see Table 21).
2. The SOX28 package includes an embedded 32,768 Hz crystal.
3. Not recommended for new design. Contact local ST sales office for availability.
Caution:
Do not place the SNAPHAT® battery package “M4Txx-BR12SH” in conductive foam as it will
drain the lithium button-cell battery.
For other options, or for more information on any aspect of this device, please contact the ST sales office
nearest you.
Table 21.
SNAPHAT® battery/crystal table
Part number
40/43
Description
Package
M4T28-BR12SH
Lithium battery (48 mAh) and crystal SNAPHAT® top
SH
M4T32-BR12SH
Lithium battery (120 mAh) and crystal SNAPHAT® top
SH
Doc ID 7531 Rev 11
M41ST85W
8
Environmental information
Environmental information
Figure 27. Recycling symbols
This product contains a non-rechargeable lithium (lithium carbon monofluoride chemistry)
button cell battery fully encapsulated in the final product.
Recycle or dispose of batteries in accordance with the battery manufacturer's instructions
and local/national disposal and recycling regulations.
Doc ID 7531 Rev 11
41/43
Revision history
M41ST85W
9
Revision history
Table 22.
Document revision history
Date
Revision
Aug-2000
1
Changes
First issue
24-Aug-2000
1.1
Block diagram added (Figure 4)
12-Oct-2000
1.2
trec table removed, cross references corrected
18-Dec-2000
2
Reformatted, TOC added, and PFI input leakage current added (Table 11)
18-Jun-2001
2.1
Addition of trec information, table changed, one added (Table 2, 6); changed PFI/PFO
graphic (see Figure 4); change to DC and AC characteristics, order information
(Table 11, 12, 20); note added to “Setting Alarm Clock Registers” section; added
temp./voltage info. to tables (Table 10, 11, 6, 12, 13); addition of default values
(Table 7)
22-Jun-2001
2.2
Note added to clock operation section
26-Jul-2001
3
07-Aug-2001
3.1
Improve text in “Setting the Alarm Clock” section
20-Aug-2001
3.2
Change VPFD values in document
06-Sep-2001
3.3
DC characteristics VBAT changed; VOHB changed; PFI hysteresis (PFI Rising) spec.
added; and crystal electrical characteristics table removed (Table 11, 6)
03-Dec-2001
3.4
Changed READ/WRITE mode sequences (Figure 10, 12); change in VPFD lower limit
for 5V (M41ST85Y) part only (Table 11, 20)
01-May-2002
3.5
Change trec definition (Table 6); modify reflow time and temperature footnote (Table 8)
03-Jul-2002
3.6
Modify DC characteristics table footnote, default values (Table 11, 7)
15-Nov-2002
3.7
Added embedded crystal (MX) package option; corrected initial power-up condition
(cover page, Figure 1, 3, 4, 5, 24, Table 1, 7, 20, )
24-Jan-2003
3.8
Update diagrams (Figure 4, 5, 24); update values (Table 13, 5, 6, 7, )
25-Feb20-03
4
New Si changes (Table 13, 5, 6); corrected dimensions (Figure 24; Table )
20-May-2004
5
Reformatted; correct dimensions; update Lead-free information (Figure 20, 13, 16;
Table 8, 16, 20)
Change in product maturity
15-Jun-2004
6
Update characteristics; add package shipping (Figure 3; Table 1, 11, 20)
13-Sep-2004
7
Update maximum ratings (Table 8)
10-Jan-2006
8
Updated template, Lead-free text, removed 5V references (Figure 1, 2, 3, 4, 5; Table 5,
8, 9, 11, 12, 13, 20, 21)
03-Oct-2007
9
Reformatted document, minor textual changes; added lead-free second level
interconnect information to cover page and Section 6: Package mechanical data;
updated Table 8.
16-Dec-2008
10
Added Section 8: Environmental information; updated Table 8, Section 6: Package
mechanical data; minor reformatting.
03-Oct-2011
11
Updated Table 20: Ordering information scheme as shipping in tubes is not
recommended for new design; updated Section 8: Environmental information; added
Figure 25, 26 and Table 18, 19.
42/43
Doc ID 7531 Rev 11
M41ST85W
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