DS1235Y

The DS1235Y has the following features including Data retention in the absence of Vcc;Data is automatically protected during power loss;Directly replaces 32K x 8 volatile static RAMs or EEPROMs;Unlimited write cycles;Low-ewer CMOS;Over 5 years of data retention;Standard 28-pin JEDEC pinout;Available in 100, 120, 1 b0, and 200 ns read access times;Read cycle time equals write cycle time;Lithium energy source is electrically disconnected to retain freshness until power is applied for the first time.

The DS1235Y 256K Nonvolatile SRAM is a 262, 144-b i t, fully static SRAM organized as 32,768 words by 8 bits. The nonvolatile memory has a self-contained lithium energy source and control circuitry that constantly monitors Vcc for an out-of-tolerance condition.  When such a condition occurs, the lithium energy source is automatically switched on and write protection is unconditionally enabled to prevent garbled data.The nonvolatile SRAM can be used in place of existing 32K x 8 SRAMs directly conforming to the popular bytewide 28256 EEPROM, allowing direct substitution white enhancing performance. There is no limit on the number of write cycles that can be executed and no additional support circuitry is required for microprocessor interface.The DS1235Y is shipped from Dallas Semiconductor with the lithium energy source disconnetted,  guaranteeing  full  energy  capacity.When Vcc is first applied at a level of greater than Vtp1,the lithium energy source is enabled for battery backup operation.

Battery redundancy ensures reliability.The DS1235Y contains two lithium energy cells separated by an internal isolation switch. During battery backup time the cell with the highest voltage is selected for use. If one battery fails,the other battery automatically takes over. The switch between batteries is transparent to the user.This is a stress rating only and functional operation of the device at these or any other conditions outside those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.