RTC DS 12C887 is widely used to provide exact time and date in many applications such as x86 IBM PC. This RTC provides time components hour, minute and second in addition to the date/calendar components of year, month and day. This chip uses an internal lithium battery, which keeps the time and date updated even when the power is off. The DS12C887 works on CMOS technology to keep the power consumption low. It has a total of 128 bytes of non volatile RAM. It uses 14 bytes of RAM for storing the values of clock/calendar and control registers. The rest 114 bytes of RAM are for general purpose data storage.

The internal registers are accessible only when the RTC is powered by an external power source. When the external power is turned off, the RTC clock keeps running from the internal lithium battery source but the internal registers of the RTC cannot be accessed. RTC 12C887 becomes active when a voltage greater than 4.25V is applied and the internal registers can be accessed after 200 msec.

Features:-

• Drop-in replacement for IBM AT computer clock/calendar
• Pin compatible with the MC146818B and DS1287
• Totally nonvolatile with over 10 years of operation in the absence of power
• Self-contained subsystem includes lithium,quartz, and support circuitry.
• Counts seconds, minutes, hours, days, day of the week, date, month, and year with leap year compensation valid up to 2100
• Binary or BCD representation of time, calendar, and alarm
• 12– or 24–hour clock with AM and PM in 12–hour mode
• Daylight Savings Time option
• Selectable between Motorola and Intel bus timing
• Multiplex bus for pin efficiency
• Interfaced with software as 128 RAM locations

          – 15 bytes of clock and control registers

          – 113 bytes of general purpose RAM

• Programmable square wave output signal
• Bus–compatible interrupt signals (IRQ)
• Three interrupts are separately software maskable and testable

          – Time–of–day alarm once/second to once/day

          – Periodic rates from 122 ms to 500 ms

          – End of clock update cycle 

• Century register

Related Document:-

 DS12C887 IC Data Sheet