DESCRIPTION
The DS1321 Flexible Nonvolatile Controller with Lithium Battery Monitor is a CMOS circuit which solves the application problem of converting CMOS SRAMs into nonvolatile memory. Incoming power is monitored for an out-of-tolerance condition. When such a condition is detected, chip enable outputs are inhibited to accomplish write protection and the battery is switched on to supply the SRAMs with uninterrupted power. Special circuitry uses a low-leakage CMOS process which affords precise voltage detection at extremely low battery consumption. One DS1321 can support as many as four SRAMs arranged in any of three memory configurations.

FEATURES
■ Converts CMOS SRAM into nonvolatile
   memory
■ Unconditionally write-protects SRAM when
   VCC is out of tolerance
■ Automatically switches to battery backup
   supply when VCC power failure occurs
■ Flexible memory organization
   - Mode 0: 4 banks with 1 SRAM each
   - Mode 1: 2 banks with 2 SRAMs each
   - Mode 2: 1 bank with 4 SRAMs each
■ Monitors voltage of a lithium cell and
   provides advanced warning of impending
   battery failure
■ Signals low-battery condition on active low
   Battery Warning output signal
■ Resets processor when power failure occurs
   and holds processor in reset during system
   power-up
■ Optional 5% or 10% power-fail detection
■ 16-pin PDIP, 16-pin SO and 20-pin TSSOP
   packages
■ Industrial temperature range of -40°C to
   +85°C