DS12885Q/T&R

Overview

The DS12885Q is a real-time clock and calendar integrated circuit designed as a direct replacement for legacy IBM AT computer clocks. It features a parallel interface with multiplexed address/data lines, housed in a 28-pin PLCC package. The device maintains time in binary or BCD format, supporting 12/24-hour modes and automatic leap year correction through 2100. It includes 114 bytes of battery-backed static RAM, accessible via specific address logic levels. Power supply ranges from 4.5 V to 5.5 V, with a backup battery range of 2.5 V to 4 V. Maximum timing current is 15 mA at 5.5 V. Operating temperature spans 0°C to 70°C.

Feature Summary

• Direct drop-in replacement for DS1285 and MC146818B with identical form, fit, and function.
• Integrated 114-byte battery-backed NVSRAM with selectable access via AD6 pin logic level.
• Automatic date adjustment for month lengths and leap years valid up to the year 2100.
• Programmable square-wave output and three maskable interrupts with common IRQ line.

Applications

• IBM AT compatible computer systems requiring RTC functionality.
• Industrial control systems needing precise timekeeping with non-volatile memory.
• Data logging equipment requiring calendar tracking and alarm capabilities.

Procurement Notes

Verify the suffix 'T&R' indicates tape-and-reel packaging configuration. Confirm RoHS compliance status, as older revisions may not meet current environmental standards. Check manufacturer obsolescence notices, as this component family has faced discontinuation risks. Ensure voltage levels match system requirements before integration.

Selection Notes

Select the Q variant for surface-mount PLCC applications. Verify interface compatibility with Intel or Motorola bus timing modes if interfacing with legacy processors. Consider the DS12887 if an integrated quartz crystal and lithium source are required instead of external components. Validate backup battery voltage range against available coin-cell options.

Part Context

The DS12885 series belongs to the Dallas Semiconductor (now Maxim Integrated) RTC family, succeeding the DS1285. It provides enhanced RAM capacity compared to its predecessor while maintaining pin compatibility. The Q+ designation typically indicates lead-free manufacturing compliant with RoHS directives.

Replacement Considerations

DS12885S+ offers a SO-24 package alternative. DS12885SN+ provides an industrial temperature range (-40°C to +85°C). DS12887 integrates the crystal and battery directly into the package.