Document Number: 001-55720 Rev. *H Page 5 of 28
it only when the STORE is complete. Upon completion of the
STORE operation, the nvSRAM memory access is inhibited for
t
LZHSB
time after 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
(V
CC
<V
SWITCH
), an internal RECALL request is latched. When
V
CC
again exceeds the V
SWITCH
on powerup, a RECALL cycle
is automatically initiated and takes t
HRECALL
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 CY14B256KA 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 0x0E38 Valid READ
2. Read address 0x31C7 Valid READ
3. Read address 0x03E0 Valid READ
4. Read address 0x3C1F Valid READ
5. Read address 0x303F Valid READ
6. Read address 0x0FC0 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 t
STORE
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,
the following sequence of CE
or OE controlled read operations
must be performed:
1. Read address 0x0E38 Valid READ
2. Read address 0x31C7 Valid READ
3. Read address 0x03E0 Valid READ
4. Read address 0x3C1F Valid READ
5. Read address 0x303F Valid READ
6. Read address 0x0C63 Initiate RECALL cycle
Internally, RECALL is a two step procedure. First, the SRAM data
is cleared. Next, the nonvolatile information is transferred into the
SRAM cells. After the t
RECALL
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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