m41st84w STMicroelectronics, m41st84w Datasheet - Page 4

• Manufacturer Part Number: m41st84w
• Description: 3.0/3.3v I 2c Serial Rtc With Supervisory Functions
• Manufacturer: STMicroelectronics

M41ST84W
SUMMARY DESCRIPTION
The M41ST84W Serial Real-Time Clock is built in
a low power CMOS SRAM process. It has a 64-
byte memory space with 44 bytes of NVRAM and
20 memory-mapped RTC registers (see
3., page
binary coded decimal (BCD) format.
A built-in, low power 32.768kHz oscillator (external
crystal controlled) provides the time base for the
timekeeping and calendar functions.
The basic clock/calendar functions are handled by
the first eight RTC registers, while the other twelve
bytes provide status/control for the Alarm, Watch-
dog, and Square Wave functions.
Addresses and data are transferred serially via the
two line, bi-directional I
address register is incremented automatically af-
ter each WRITE or READ data byte.
Figure 2. Logic Diagram
4/29
RSTIN
SDA
SCL
WDI
PFI
XO
XI
14). The RTC registers are configured in
V CC
M41ST84W
V SS
2
V BAT
C interface. The built-in
RST
IRQ/FT/OUT
SQW
PFO
AI03677
Table
The M41ST84W 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-volatile, time-of-day clock/calendar, Alarm
interrupts, Watchdog Timer and programmable
Square Wave output. Other features include a
Power-On Reset as well as an additional input
(RSTIN) which can also generate an output Reset
(RST). The eight clock address locations contain
the century, year, month, date, day, hour, minute,
second and tenths/hundredths of a second in 24
hour BCD format. Corrections for 28, 29 (leap year
- valid until year 2100), 30 and 31 day months are
made automatically.
The M41ST84W is supplied in a 16-lead SOIC
package.
Table 1. Signal Names
XI
XO
IRQ/FT/OUT
PFI
PFO
RST
RSTIN
SCL
SDA
SQW
WDI
V
V
V
NC
CC
BAT
SS
Oscillator Input
Oscillator Output
Interrupt/Frequency Test/Out
Output (Open Drain)
Power Fail Input
Power Fail Output
Reset Output (Open Drain)
Reset Input
Serial Clock Input
Serial Data Input/Output
Square Wave Output
Watchdog Input
Supply Voltage
Battery Supply Voltage
Ground
No Connect