DS12885SN+

Overview

The DS12885SN+ is a real-time clock and calendar IC manufactured by Analog Devices Inc./Maxim Integrated. It provides timekeeping for seconds, minutes, hours, day, date, month, and year with automatic leap year compensation through 2099. The device includes 114 bytes of battery-backed static RAM and supports both Intel and Motorola bus timing modes via a multiplexed parallel interface. It operates on a primary supply of 4.5V to 5.5V and switches automatically to a backup supply (2.5V to 4V) upon power failure. The component is housed in a 24-SOIC surface-mount package.

Feature Summary

• Multiplexed byte-wide parallel interface supporting Intel and Motorola bus timing modes
• Automatic power-fail detection and switching circuitry between VCC and VBAT supplies
• 114 bytes of nonvolatile, battery-backed static RAM accessible as 128 logical locations
• Programmable square-wave output and one time-of-day alarm with maskable interrupts

Applications

• Embedded systems requiring precise timekeeping
• Utility meters for data logging and timestamping
• Security systems needing event recording
• Network hubs, bridges, and routers for synchronization

Procurement Notes

Verify the specific suffix 'SN+' indicates RoHS compliance and lead-free status according to manufacturer documentation. Confirm the 24-SOIC package dimensions match the design footprint. Ensure the external 32.768kHz crystal meets the specified load capacitance requirements for proper oscillator startup.

Selection Notes

Select this part when a drop-in replacement for legacy IBM AT clock/calendar designs is required. Choose the industrial temperature range (-40°C to +85°C) variant if operating conditions exceed commercial limits. Verify that the system architecture supports the required parallel address/data bus timing modes.

Part Context

The DS12885 family serves as a direct replacement for the DS1285 and DS1287 models. Unlike the DS12887, which integrates a crystal and battery, the DS12885 requires an external 32.768kHz quartz crystal connected to pins X1 and X2. The SN+ designation identifies the specific SOIC package version within the broader DS12885 product line.

Replacement Considerations

The M48T86MH1E is listed as a substitute option. Note that the M48T86MH1E uses a 28-SOP package with a Snaphat socket, differing from the 24-SOIC form factor of the DS12885SN+. Electrical parameters and pinouts are not directly compatible without hardware redesign.