Rainbow Electronics DS1250Y_AB - Manual (Page 2)

DS1250Y/AB
041497 2/11
DESCRIPTION
The DS1250 4096K Nonvolatile SRAMs are
4,194,304–bit, fully static, nonvolatile SRAMs orga-
nized as 524,288 words by 8 bits. Each complete NV
SRAM has a self–contained lithium energy source and
control circuitry which constantly monitors V
CC
for an
out–of–tolerance condition. When such a condition oc-
curs, the lithium energy source is automatically
switched on and write protection is unconditionally en-
abled to prevent data corruption. DIP–package
DS1250 devices can be used in place of existing 512K x
8 static RAMs directly conforming to the popular byte-
wide 32–pin DIP standard. DS1250 devices in the Pow-
erCap Module package are directly surface mountable
and are normally paired with a DS9034PC PowerCap to
form a complete Nonvolatile SRAM module. There is no
limit on the number of write cycles that can be executed
and no additional support circuitry is required for micro-
processor interfacing.
READ MODE
The DS1250 devices execute a read cycle whenever
WE (Write Enable) is inactive (high) and CE (Chip En-
able) and OE (Output Enable) are active (low). The
unique address specified by the 19 address inputs (A
0
–
A
18
) defines which of the 524,288 bytes of data is to be
accessed. Valid data will be available to the eight data
output drivers within t
ACC
(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 t
CO
for CE or t
OE
for OE rather than address access.
WRITE MODE
The DS1250 devices execute a write cycle whenever
the WE and CE signals are active (low) after address in-
puts 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 (t
WR
) before another cycle can
be initiated. The OE control signal should be kept inac-
tive (high) during write cycles to avoid bus contention.
However, if the output drivers are enabled (CE and OE
active) then WE will disable the outputs in t
ODW
from its
falling edge.
DATA RETENTION MODE
The DS1250AB provides full functional capability for
V
CC
greater than 4.75 volts and write protects by
4.5 volts. The DS1250Y provides full functional capabil-
ity for V
CC
greater than 4.5 volts and write protects by
4.25 volts. Data is maintained in the absence of V
CC
without any additional support circuitry. The nonvolatile
static RAMs constantly monitor V
CC
. Should the supply
voltage decay, the NV SRAMs automatically write pro-
tect themselves, all inputs become “don’t care,” and all
outputs become high impedance. As V
CC
falls below
approximately 3.0 volts, a power switching circuit con-
nects the lithium energy source to RAM to retain data.
During power–up, when V
CC
rises above approximately
3.0 volts, the power switching circuit connects external
V
CC
to RAM and disconnects the lithium energy source.
Normal RAM operation can resume after V
CC
exceeds
4.75 volts for the DS1250AB and 4.5 volts for the
DS1250Y.
FRESHNESS SEAL
Each DS1250 device is shipped from Dallas Semicon-
ductor with its lithium energy source disconnected,
guaranteeing full energy capacity. When V
CC
is first
applied at a level greater than 4.25 volts, the lithium en-
ergy source is enabled for battery back–up operation.
PACKAGES
The DS1250 devices are available in two packages:
32–pin DIP and 34–pin PowerCap Module (PCM). The
32–pin DIP integrates a lithium battery, an SRAM
memory and a nonvolatile control function into a single
package with a JEDEC–standard 600 mil DIP pinout.
The 34–pin PowerCap Module integrates SRAM
memory and nonvolatile control along with contacts for
connection to the lithium battery in the DS9034PC Pow-
erCap. The PowerCap Module package design allows
a DS1250 PCM device to be surface mounted without
subjecting its lithium backup battery to destructive high–
temperature reflow soldering. After a DS1250 PCM is
reflow soldered, a DS9034PC PowerCap is snapped on
top of the PCM to form a complete Nonvolatile SRAM
module. The DS9034PC is keyed to prevent improper
attachment. DS1250 PowerCap Modules and
DS9034PC PowerCaps are ordered separately and
shipped in separate containers. See the DS9034PC
data sheet for further information.