M41T56C64

Summary description

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Summary description

The M41T56C64 is a low power, Serial Real Time Clock with 56 bytes of NVRAM 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 M41T56C64 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 RAM and clock operations can be supplied from a small lithium coin cell.

Typical data retention time for the Serial RTC is in excess of 10 years with a 50mAh, 3V

lithium cell. The M41T56C64 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

M41T56

+

M24C64

(EEPROM)

SCL

WC

SDA

FT/OUT

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