DS12C887

DS12C887 is a Dallas/Maxim CMOS real-time clock/calendar (RTC) with battery-backed RAM. It keeps system time when main power is off and is commonly used in PCs and embedded systems.
Key features:
- Timekeeping: seconds, minutes, hours, day, date, month, year with leap-year handling; typically uses a 32.768 kHz clock.
- Alarm and periodic interrupts: can generate IRQs to wake or alert the host.
- Battery-backed RAM (NVRAM): stores configuration/data that must survive power loss.
- Interface: accessed via a simple register interface (in PCs, via CMOS-style ports; compatible with legacy RTCs like DS1287/DS12887).
- Applications: motherboard RTCs, embedded controllers, any system requiring persistent timekeeping without continuous power.
Notes:
- Often used as a drop-in or compatible replacement for older RTCs.
- Requires a backup battery to retain time and NVRAM data when Vcc is removed.

Equivalents/compatible parts include the MC146818A (Intel original RTC) and Dallas’ RAM-backed RTCs DS1287 and DS1286. The DS12C887 is a CMOS, pin/register-compatible variant of the MC146818A family, so these are generally interchangeable for PC-style real-time clocks.

Concise features of DS12C887 (RTC/CMOS):
- Real-time clock and calendar: seconds, minutes, hours, day of week, date, month, year; supports 12/24-hour modes with leap-year correction.
- Data formats: RTC data can be in binary or BCD.
- Battery-backed operation: preserves time and CMOS RAM when Vcc is off; includes trickle-charge support for an external battery.
- CMOS RAM: battery-backed memory for user data storage.
- Interrupts: programmable alarm/interrupt capability; generates IRQs to the CPU.
- Periodic and update interrupts: supports periodic timebase interrupts plus end-of-update signaling.
- Square-wave output: selectable frequencies for clock-out signal.
- PC-compatible register map: same CMOS/I/O interface as the MC146818A, accessible via standard CMOS addresses (0x70/0x71).
- Optional features: supports language-free, low-power operation typical of classic RTCs.

- Pin count: 28 pins (DIP/SOIC).
- Function: Real-Time Clock/Calendar with battery-backed CMOS RAM and alarm/interrupt features; keeps time (seconds, minutes, hours, day/date/month/year) using a 32.768 kHz oscillator, even when main power is off.

- Manufacturer: Dallas Semiconductor (often listed as Dallas) for the DS12C887. Today, Dallas Semiconductor is part of Maxim Integrated.
- What kind of company: A semiconductor company that designs and manufactures integrated circuits and related electronic components (timing/RTC ICs, memory, iButton products, etc.).

- Real-time clock/calendar in PC-compatible boards and embedded controllers
- Battery-backed non-volatile RAM for config, calibration data, logs in data loggers and measurement systems
- Time stamping and scheduling in industrial automation, telecom, POS terminals, and network equipment
- Wake-up alarms and periodic interrupts for power management and event-driven control
- Any device requiring accurate, low-power timekeeping with power-loss survivability (e.g., embedded systems, remote telemetry)

DS12C887 is a 28-pin real-time clock. It’s available in DIP-28 (through-hole) and 28-pin surface-mount packages, such as SOIC-28.