The **DS14285SN** is a Real-Time Clock (RTC) integrated circuit manufactured by Maxim Integrated (formerly Dallas Semiconductor). It is designed to be a pin-compatible replacement for the industry-standard DS12885, but with the addition of **NV RAM control circuitry**. --- ## 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Supply Voltage (Vcc)** | 4.5V to 5.5V | | **Interface** | Multiplexed Bus (Intel/Motorola) | | **Package Type** | 24-pin SOIC (Small Outline Integrated Circuit) | | **Operating Temp** | 0°C to +70°C | | **RAM Capacity** | 114 Bytes of User NV RAM | | **Clock Format** | BCD or Binary (12/24 Hour) | --- ## 2. Core Functional Components The internal architecture of the DS14285SN consists of several critical subsystems: ### A. Timekeeping and Calendar The device tracks seconds, minutes, hours, day of the week, date, month, and year. It features: * **Leap Year Compensation:** Valid up to the year 2100. * **Daylight Savings Support:** Programmable adjustment logic. ### B. Multiplexed Bus Interface The chip is designed to interface directly with microprocessors that use a multiplexed address/data bus (such as the 8051 or 68HC11). It supports both **Intel** and **Motorola** bus timing. ### C. Power Management and NV RAM Control This is the "S" variant's specialty. It includes: * **Backup Battery Input:** A pin for a 3V lithium cell to keep the clock running during power-offs. * **Write Protection:** Automatically inhibits access to the internal RAM and registers when $V_{CC}$ falls out of tolerance (brownout protection). * **External NV RAM Support:** It can provide a chip-enable signal to control external SRAM, effectively turning standard SRAM into Non-Volatile RAM. ### D. Interrupt Logic The device can trigger hardware interrupts based on: 1. **Alarm:** Time of day match. 2. **Periodic Rate:** Programmable from 122 $\mu s$ to 500 ms. 3. **Update Ended:** Signifies the timekeeping registers are stable for reading. --- ## 3. Pin Configuration Highlights | Pin | Name | Description | | :--- | :--- | :--- | | **1** | MOT | Bus Type Selection (High = Motorola, Low = Intel) | | **2-3** | X1, X2 | 32.768 kHz Crystal Inputs | | **4-11** | AD0-AD7 | Multiplexed Address/Data Bus | | **14** | /PWRDN | Power Down Monitor Input | | **20** | V_BAT | +3V Lithium Battery Input | | **24** | Vcc | +5V Main Power Supply | --- ## 4. Application Areas * **Legacy Computing:** Motherboards and industrial PCs. * **Embedded Systems:** Data loggers and controllers requiring time-stamping. * **Telecommunications:** Network switches and routers for log management.