Summary description
The M41T56 is a low power, Serial Real Time Clock with 56 bytes of NVRAM. A built-in 32,768Hz oscillator (external 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 M41T56 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 is in excess of 10 years with a 50mAh, 3V lithium cell. The M41T56 is supplied in an 8-lead Plastic SOIC package or a 28-lead SNAPHAT® package.
The 28-pin, 330mil SOIC provides sockets with gold plated contacts at both ends for direct connection to a separate SNAPHAT housing containing the battery and crystal. The unique design allows the SNAPHAT battery 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 surface-mounting. The SNAPHAT housing is keyed to prevent reverse insertion. The SOIC and battery/crystal packages are shipped separately in plastic anti-static tubes or in Tape & Reel form.

FEATURE summary
■ Counters for seconds, minutes, hours, day, date, month, years, and century
■ 32 KHz crystal oscillator integrating load capacitance (12.5pF) providing exceptional oscillator stability and high crystal series resistance operation
■ Serial interface supports I2C Bus (400kHz protocol)
■ Ultra-low battery supply current of 450nA (typ@3V)
■ 5V ±10% supply voltage
■ Timekeeping down to 2.5V
■ Automatic power-fail detect and switch circuitry
■ 56 bytes of general purpose RAM
■ Software clock calibration to compensate crystal deviation due to temperature
■ Automatic leap year compensation
■ Operating temperature of –40 to 85°C
■ Packaging options include:
   – 28-lead SOIC and SNAPHAT® TOP (to be ordered separately)
   – SO8N