DS1230Y/AB
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DESCRIPTION
The DS1230 256k Nonvolatile SRAMs are 262,144-bit, fully static, nonvolatile SRAMs organized as
32,768 words by 8 bits. Each NV SRAM has a self-contained lithium ener gy source and control circuitry
which 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 data corruption. DIP-package DS1230 devices can be used in place of existing 32k x 8 static
RAMs directly conforming to the popular b ytewide 28-pin DIP standard. The DIP devices also match the
pinout of 28256 EEPROMs, allowing direct substitution while enhancing performance. DS1230 devices
in the Low Profile Module package are sp ecifically designed for surfa ce-mount applications. There is no
limit on the number of write cycles that can be executed and no additional support circuitry is required for
microprocessor interfacing.
READ MODE
The DS1230 devices ex ecute a read cycle whenever WE (Write Enable) is inactive (high) and CE (Chip
Enable) and OE (Output Enable) are active (low). The unique address specified by the 15 address inputs
(A0 - A14) defines which of the 32,768 b ytes of data is to be a ccessed. Valid data will be available to the
eight data output drivers within tACC (Access Time) after the last address input signal is stable, providing
that CE and OE (Output Enable) access times are also satisfied. If OE and CE access times are not
satisfied, then data access must be measured from the later-occurring signal (CE or OE ) and the limiting
parameter is either tCO for CE or tOE for OE rather than address access.
WRITE MODE
The DS1230 devices execute a write cycle whenever the WE and CE signals are active (low) after
address inputs are stable. The later-occurring falling edge of CE or WE will determine the start of the
write cycle. The write cycle is terminated by the earlier rising edge of CE or WE . All address inputs must
be kept valid throughout the write cycle. WE must return to the high state for a minimum recovery time
(tWR) before another cycle can be initiated. The OE control signal should be kept inactive (high) during
write cycles to avoid bus contention. However, if the output drivers are enabl ed (CE and OE acti ve) t h en
WE will disable the outputs in tODW from its falling edge.
DATA RETENTION MODE
The DS1230AB provides full functional capability for VCC greater than 4.75 volts and write protects by
4.5 volts. The DS1230Y provides full functional capability for VCC greater than 4.5 volts and write
protects by 4.25 volts. Data is maintained in the absence of VCC without an y additional support circuitry.
The nonvolatile static RAMs constantly monitor VCC. Should the supply voltage decay, the NV SRAMs
automatically write protect themselves, all inputs become “don’t care,” and all outputs become high-
impedance. As VCC falls below approximately 3.0 volts, a power switching circuit connects the lithium
energy source to RAM to retain data. During power-up, when VCC rises above approximately 3.0 volts
the power switching circuit connects external VCC to RAM and disconnects the lithium energy source.
Normal RAM operation can resum e after VCC exceeds 4.75 volts for the DS1230AB and 4.5 volts for the
DS1230Y.
FRESHNESS SEAL
Each DS1230 device is shipped from Dallas Semiconductor with its lithium energy source disconnected,
guaranteeing full ener gy capacit y. When VCC is first applied at a level greater than 4.25 volts, the lithium
energy source is enabled for battery back-up operation.