CY14B104LA, CY14B104NA
Document #: 001-49918 Rev. *B
Page 4 of 23
Device Operation
The CY14B104LA/CY14B104NA 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
CY14B104LA/CY14B104NA 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 on page
16 for a complete description of read and write modes.
SRAM Read
The CY14B104LA/CY14B104NA performs a read cycle when
CE and OE are LOW and WE and HSB are HIGH. The address
specified on pins A0-18 or A0-17 determines which of the 524,288
data bytes or 262,144 words of 16 bits each are accessed. Byte
enables (BHE, BLE) determine which bytes are enabled to the
output, in the case of 16-bit words. 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.
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 DQ0–15
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. The Byte Enable inputs (BHE, BLE) determine which bytes
are written, in the case of 16-bit words. 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.
AutoStore Operation
The CY14B104LA/CY14B104NA 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 CY14B104LA/CY14B104NA.
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.
Note If the capacitor is not connected to VCAP pin, AutoStore
must be disabled using the soft sequence specified in Preventing
AutoStore on page 6. In case AutoStore is enabled without a
capacitor on VCAP pin, the device will attempt an AutoStore
operation without sufficient charge to complete the Store. This
may corrupt the data stored in nvSRAM.
Figure 4 shows the proper connection of the storage capacitor
(VCAP) for automatic store operation. Refer to DC Electrical
Characteristics on page 8 for the size of VCAP. The voltage on
the VCAP pin is driven to VCC by a regulator on the chip. A pull
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.
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.
Figure 4. AutoStore Mode
Hardware STORE Operation
The CY14B104LA/CY14B104NA 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 CY14B104LA/CY14B104NA conditionally
initiates a STORE operation after tDELAY. 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.
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
CY14B104LA/CY14B104NA 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 CY14B104LA/CY14B104NA. But any SRAM read
and write cycles are inhibited until HSB is returned HIGH by MPU
or other external source.
0.1uF
Vcc
V
CAP
Vcc
WE
V
CAP
V
SS
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