AUSTIN SEMICONDUCTOR, INC.
ADVANCE INFORMATION
nvSRAM
AS8nvLC512K32
Austin Semiconductor, Inc.
for automatic store operation. Refer to DC Electrical Characteristics
for the size of VCAP. The voltage on the VCAP pin is driven to VCC
by a regulator on the chip. Apull up should be placed on WE\ to hold
it inactive during power up. This pull up is effective only if the WE\
signal is tri-state during power up. Many MPUs tri-state their
controls on power up. This should be verified when using the pull
up. When the nvSRAM comes out of power-on-recall, the MPU
must be active or the WE\ held inactive until the MPU comes out of
reset.
Device Operation
The AS8nvLC512K32 nvSRAM is made up of two functional
components paired in the same physical cell. They are
a SRAM memory cell and a nonvolatile QuantumTrap cell. The SRAM
memory cell operates as a standard fast static RAM. Data in the
SRAM is transferred to the nonvolatile cell (the STORE operation),
or from the nonvolatile cell to the SRAM (the RECALL operation).
Using this unique architecture, all cells are stored and recalled in
parallel. During the STORE and RECALL operations, SRAM read
and write operations are inhibited. The AS8nvLC512K32 supports
infinite reads and writes similar to a typical SRAM. In addition, it
provides infinite RECALL operations from the nonvolatile cells and
up to 200K STORE operations. See the Truth Table For SRAM
Operations for a complete description of read and write modes.
To reduce unnecessary nonvolatile stores, AutoStore and hardware
store operations are ignored unless at least one write operation has
taken place since the most recent STORE or RECALL cycle. Software
initiated STORE cycles are performed regardless of whether a write
operation has taken place. The HSB\ signal is monitored by the
system to detect if an AutoStore cycle is in progress.
SRAM Read
The AS8nvLC512K32 performs a read cycle when CE\ and OE\ are
LOW and WE\ and HSB\ are HIGH. The address specified on pins
A0-18 determines which of the 524,288 data bytes. When the read is
initiated by an address transition, the outputs are valid after a delay
of tAA (read cycle 1). If the read is initiated by CE\ or OE\, the outputs
are valid at tACE or at tDOE, whichever is later (read cycle 2). The data
output repeatedly responds to address changes within the tAA access
time without the need for transitions on any control input pins. This
remains valid until another address change or until CE\ or OE\ is
brought HIGH, or WE\ or HSB\ is brought LOW.
Figure 2. AutoStore Mode
Vcc
0.1uF
Vcc
WE1-4
VCAP
VCAP
VSS
SRAM Write
A write cycle is performed when CE\ and WE\ are LOW and HSB\ is
HIGH. The address inputs must be stable before entering the write
cycle and must remain stable until CE\ or WE\ goes HIGH at the end
of the cycle. The data on the common I/O pins DQ0–31 are written
into the memory if the data is valid tSD before the end of a WE\
controlled write or before the end of an CE\ controlled write. It is
recommended that OE\ be kept HIGH during the entire write cycle to
avoid data bus contention on common I/O lines. If OE\ is left LOW,
internal circuitry turns off the output buffers tHZWE after WE\ goes
LOW.
Hardware STORE Operation
The AS8nvLC512K32 provides the HSB\6 pin to control and
acknowledge the STORE operations. Use the HSB\ pin to request a
hardware STORE cycle. When the HSB pin is driven LOW, the
AS8nvLC512K32 conditionally initiates a STORE operation after
t
DELAY.An actual STORE cycle only begins if a write to the SRAM has
taken place since the last STORE or RECALL cycle. The HSB\ pin
also acts as an open drain driver that is internally driven LOW to
indicate a busy condition when the STORE (initiated by any means)
is in progress.
AutoStore Operation
The AS8nvLC512K32 stores data to the nvSRAM using one of the
following three storage operations: Hardware Store activated by HSB\;
Software Store activated by an address sequence;AutoStore on device
power down. The AutoStore operation is a unique feature of
QuantumTrap technology and is enabled by default on the
AS8nvLC512K32.
SRAM read and write operations that are in progress when HSB is
driven LOW by any means are given time to complete before the
STORE operation is initiated. After HSB\ goes LOW, the
AS8nvLC512K32 continues SRAM operations for tDELAY. If a write
is in progress when HSB\ is pulled LOW it is enabled a time, tDELAY to
complete. However, any SRAM write cycles requested after HSB\
goes LOW are inhibited until HSB\ returns HIGH. In case the write
latch is not set, HSB\ is not driven LOW by the AS8nvLC512K32.
But any SRAM read and write cycles are inhibited until HSB\ is
returned HIGH by MPU or other external source.
During a normal operation, the device draws current from VCC to
charge a capacitor connected to the VCAP pin. This stored charge is
used by the chip to perform a single STORE operation. If the voltage
on the VCC pin drops below VSWITCH, the part automatically disconnects
the VCAP pin from VCC. A STORE operation is initiated with power
provided by the VCAP capacitor.
During any STORE operation, regardless of how it is initiated, the
AS8nvLC512K32 continues to drive the HSB\ pin LOW, releasing it
only when the STORE is complete. When the STORE operation is
completed, the AS8nvLC512K32 remains disabled until the HSB\
pin returns HIGH. Leave the HSB\ unconnected if it is not used..
Figure 2 shows the proper connection of the storage capacitor (VCAP
)
Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.
AS8nvLC512K32
Rev. 0.0 08/09
3
AUSTIN [ AUSTIN SEMICONDUCTOR ]
