BQ3285P-SB2

The BQ3285P-SB2 is a CMOS real-time clock/calendar peripheral from Texas Instruments, designed as a direct replacement for IBM AT-compatible computers and other applications. It provides 114 bytes of general nonvolatile storage (NVSRAM) for data retention during power loss. The device operates with a 5V supply (VCC) and a 3V backup battery (BC) to maintain timekeeping and data when main power is removed.

Key features include a parallel interface with selectable Intel or Motorola bus timing, a 160ns cycle time for fast bus operation, and support for BCD or binary clock/calendar data formats. The clock/calendar tracks seconds, minutes, hours, day of week, date, month, and year with automatic leap-year adjustment. It offers 12- or 24-hour time format, optional daylight saving adjustment, and a programmable square wave output. Three individually maskable interrupt flags provide periodic rates from 122µs to 500ms, time-of-day alarm, and end-of-clock update cycle.

The BQ3285P-SB2 is housed in a 24-pin PDIP (0.600", 15.24mm) through-hole package and operates over a temperature range of 0°C to 70°C. It requires only an external 32.768kHz crystal and a backup battery for full functionality. The device is functionally compatible with the DS1285 and closely matches the MC146818A pin configuration.