CY14B108K, CY14B108M
Document #: 001-47378 Rev. *B
Page 4 of 29
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 only effective if the WE signal is tristate during
power up. Many MPUs tristate their controls on power up. Verify
this 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.
Hardware STORE (HSB) Operation
The CY14B108K/CY14B108M provides the HSB pin to control
and acknowledge the STORE operations. The HSB pin is used
to request a Hardware STORE cycle. When the HSB pin is driven
LOW, the CY14B108K/CY14B108M conditionally initiates a
STORE operation after tDELAY. An actual STORE cycle begins
only 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 write operations that are in progress when HSB is driven
LOW by any means are given time (tDELAY) to complete before
the STORE operation is initiated. 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 CY14B108K/CY14B108M. But any SRAM read and
write cycles are inhibited until HSB is returned HIGH by MPU or
other external source.
During any STORE operation, regardless of how it is initiated,
the CY14B108K/CY14B108M continues to drive the HSB pin
LOW, releasing it only when the STORE is complete. Upon
completion
of
the
STORE
operation,
the
CY14B108K/CY14B108M remains disabled until the HSB pin
returns HIGH. Leave the HSB unconnected if it is not used.
Hardware RECALL (Power Up)
During power up or after any low power condition
(VCC<VSWITCH), an internal RECALL request is latched. When
VCC again exceeds the VSWITCH on powerup, a RECALL cycle
is automatically initiated and takes tHRECALL to complete. During
this time, the HSB pin is driven LOW by the HSB driver and all
reads and writes to nvSRAM are inhibited.
Software STORE
Data is transferred from the SRAM to the nonvolatile memory by
a software address sequence. The CY14B108K/CY14B108M
Software STORE cycle is initiated by executing sequential CE or
OE controlled read cycles from six specific address locations in
exact order. During the STORE cycle, an erase of the previous
nonvolatile data is first performed, followed by a program of the
nonvolatile elements. After a STORE cycle is initiated, further
input and output are disabled until the cycle is completed.
Because a sequence of reads from specific addresses is used
for STORE initiation, it is important that no other read or write
accesses intervene in the sequence, or the sequence is aborted
and no STORE or RECALL takes place.
To initiate the Software STORE cycle, the following read
sequence must be performed:
1. Read address 0x4E38 Valid READ
2. Read address 0xB1C7 Valid READ
3. Read address 0x83E0 Valid READ
4. Read address 0x7C1F Valid READ
5. Read address 0x703F Valid READ
6. Read address 0x8FC0 Initiate STORE cycle
The software sequence may be clocked with CE controlled reads
or OE controlled reads, with WE kept HIGH for all the six READ
sequences. After the sixth address in the sequence is entered,
the STORE cycle commences and the chip is disabled. HSB is
driven LOW. After the tSTORE cycle time is fulfilled, the SRAM is
activated again for the read and write operation.
Software RECALL
Data is transferred from the nonvolatile memory to the SRAM by
a software address sequence. A software RECALL cycle is
initiated with a sequence of read operations in a manner similar
to the Software STORE initiation. To initiate the RECALL cycle,
perform the following sequence of CE or OE controlled read
operations:
1. Read address 0x4E38 Valid READ
2. Read address 0xB1C7 Valid READ
3. Read address 0x83E0 Valid READ
4. Read address 0x7C1F Valid READ
5. Read address 0x703F Valid READ
6. Read address 0x4C63 Initiate RECALL cycle
Internally, RECALL is a two step procedure. First, the SRAM data
is cleared; then, the nonvolatile information is transferred into the
SRAM cells. After the tRECALL cycle time, the SRAM is again
ready for read and write operations. The RECALL operation
does not alter the data in the nonvolatile elements.
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