DS1287A Real-Time Clock (RTC) Plus RAM DIP-24 (DS1287A IC)
The DS1287A is a self-contained real-time clock and calendar module designed to be a direct replacement for the IBM AT computer clock/calendar. Housed in a specialized 24-pin DIP package, it integrates a lithium energy source, a quartz crystal, and support circuitry into a single encapsulated module. This design ensures that the device is totally nonvolatile, maintaining timekeeping and RAM data for over 10 years in the absence of external power. The "A" suffix denotes the addition of a RAM clear pin, which allows for a hardware-level reset of the internal general-purpose RAM without affecting the time registers.
This IC is a standard component for maintaining system time in legacy computing hardware and industrial controllers. It is frequently used in professional electronics restoration and DIY data-logging projects in India because it eliminates the need for an external crystal and battery holder, providing a compact and reliable timekeeping solution with 50 bytes of nonvolatile user RAM.
Key Features
- Self-Contained Subsystem: Includes internal lithium battery and quartz crystal.
- Drop-in Replacement: Directly replaces the MC146818A and standard IBM AT clock ICs.
- 10-Year Operation: Reliable timekeeping and data retention without external power.
- RAM Clear Pin: Dedicated input to quickly clear general-purpose RAM (specific to the "A" model).
- Automatic Leap Year Compensation: Valid through the year 2099.
- Multiplexed Bus: Efficient 8-bit interface for address and data.
- Three Maskable Interrupts: Support for alarms, periodic rates, and update cycles.
- Versatile Representation: Supports both Binary and BCD time formats.
Specifications
- IC Type: Real-Time Clock (RTC) with RAM
- Supply Voltage (VCC): 4.5V to 5.5V
- Battery Life: 10 Years (Minimum)
- General Purpose RAM: 50 Bytes
- Clock Format: 12-hour (with AM/PM) or 24-hour
- Accuracy: ±1 minute per month at 25 degrees Celsius
- Bus Timing: Selectable between Motorola and Intel styles
- Package Type: EDIP-24 (Encapsulated DIP)
- Mounting Type: Through-Hole
- Operating Temperature: 0 to 70 degrees Celsius
Interfaces
- Pin 1 (MOT): Bus Type Selection (GND for Intel, VCC for Motorola)
- Pin 2–3, 16, 20, 22: No Connection (NC)
- Pins 4–11 (AD0–AD7): Multiplexed Address/Data Bus
- Pin 12 (GND): Ground
- Pin 13 (CS): Chip Select (Active Low)
- Pin 14 (AS): Address Strobe
- Pin 15 (RW): Read/Write Input
- Pin 17 (DS): Data Strobe
- Pin 18 (RESET): Reset Input
- Pin 19 (IRQ): Interrupt Request Output (Open Drain)
- Pin 21 (RCLR): RAM Clear (Active Low)
- Pin 23 (SQW): Square Wave Output
- Pin 24 (VCC): Positive Supply Voltage (+5V)
