DS14285S/T&R

Real Time Clock Overview

The DS14285S/T&R is a real-time clock (RTC) with nonvolatile RAM control, designed as a direct replacement for the IBM AT computer clock. It operates on a +5V supply within an industrial temperature range of -40°C to +85°C and is housed in a 24-pin SOIC package. The device features a multiplexed address/data bus interface compatible with Intel timing standards. It provides a 100-year calendar with leap year compensation valid up to 2100, supporting both binary and BCD data formats. Internal functions include time-of-day alarms, programmable square wave generation, and three software-maskable interrupts. The RTC maintains timekeeping via an external 32.768 kHz crystal connected to X1/X2 pins and utilizes an external battery at VBAT for backup.

Real Time Clock Feature Summary

• Multiplexed Bus Interface: Utilizes AD0-AD7 for address and data sharing, operating in Intel bus timing mode without a MOT pin.
• Nonvolatile SRAM Control: Manages external SRAM write-protection and power switching via CEO and VCCO pins during power failures.
• Calendar and Alarm Functions: Supports 12/24-hour modes, daylight saving time adjustments, and once-per-second to once-per-day alarms.
• Interrupt System: Features three independent interrupt sources—alarm, periodic, and update-ended—with maskable enable bits.

Real Time Clock Applications

• IBM AT Computer Clock Replacement
• Industrial Systems Requiring Nonvolatile Timekeeping
• Embedded Controllers with External SRAM Backup

Real Time Clock Procurement Notes

Verify that the specific order includes the tape and reel packaging suffix. Confirm the industrial temperature grade (-40°C to +85°C) matches system requirements. Ensure the design accommodates external components, specifically a 32.768 kHz quartz crystal with 6 pF load capacitance and a standard 3V lithium cell for the VBAT pin.

Real Time Clock Selection Notes

Select this model over the DS14287 if an external crystal and battery are preferred or required by the board layout. This variant lacks the internal encapsulated lithium cell found in the DS14287. Ensure the application uses Intel bus timing; Motorola timing is not supported as the MOT pin is absent. Verify that the external SRAM data retention current allows for sufficient backup duration when powered by the VBAT source.

Real Time Clock Part Context

This component belongs to the DS14285/DS14287 family of real-time clocks. The 'SN' designation indicates the industrial temperature grade (-40°C to +85°C), while 'S' denotes the SOIC package. The '/T&R' suffix specifies the tape and reel shipping format. It serves as a functional successor to the DS1285/DS1287 series, offering enhanced nonvolatile memory control capabilities.

Real Time Clock Replacement Considerations

Public confirmed substitute part numbers: DS14285SN, DS14285SN+.

Real Time Clock FAQ

Does the DS14285S support Motorola bus timing?

No, the DS14285S does not have a MOT pin and operates exclusively in Intel bus timing mode.

What is the function of the VCCO pin?

The VCCO pin provides the higher of VCC or VBAT through an internal switch to power an external SRAM.

How is the oscillator configured?

An external 32.768 kHz quartz crystal with a 6 pF load capacitance must be connected directly to the X1 and X2 pins.