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M41T00SC64 Summary description
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1 Summary description
The M41T00SC64 is a low power, Serial Real Time Clock plus a 64Kb EEPROM (see
Figure 3). A built-in 32,768Hz oscillator (crystal controlled) and the first 8 bytes of the RAM
are used for the clock/calendar function and are configured in binary coded decimal (BCD)
format. Addresses and data are transferred serially via a two-line, bi-directional bus. The
built-in address register is incremented automatically after each WRITE or READ data byte.
The M41T00SC64 clock has a built-in power sense circuit which detects power failures and
automatically switches to the battery supply during power failures. The energy needed to
sustain the clock operations can be supplied from a small lithium coin cell.
Typical data retention time for the Serial RTC is in excess of 9.5 years with a 50mAh, 3V
lithium cell. The M41T00SC64 is supplied in an 18-lead Plastic SOIC package.
1.1 Calibration
As the crystal is molded together with the silicon in this package, ST can program the
appropriate calibration value necessary to achieve ±5 ppm accuracy at 25°C after two SMT
reflows (see Figure 4). This calibration value will be written into address 1550h of
the EEPROM. This clock accuracy can then be guaranteed to drift no more than ±3 ppm the
first year, and ±1 ppm for each following year due to crystal aging.
Figure 1. Logic diagram
1. Open drain output
AI09123
V
CC
M41T00S
+
M24C64
(EEPROM)
V
SS
SCL
E
0
E
1
E
2
WC
SDA
FT/OUT
(1)
V
BAT
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