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Best Practices
nvSRAM products have been used effectively for over 15
years. While ease-of-use is one of the product's main system
values, experience gained working with hundreds of applica-
tions has resulted in the following suggestions as best
practices:
■
The nonvolatile cells in an nvSRAM are programmed on the
test floor during final test and quality assurance. Incoming
inspection routines at customer or contract manufacturer's
sites sometimes reprograms these values. Final NV patterns
are typically repeating patterns of AA, 55, 00, FF, A5, or 5A.
The end product's firmware must not assume that an NV
array is in a set programmed state. Routines that check
memory content values to determine first time system config-
uration, cold or warm boot status, and so on must always
program a unique NV pattern (for example, complex 4-byte
pattern of 46 E6 49 53 hex or more random bytes) as part of
the final system manufacturing test to ensure these system
routines work consistently.
Table 1. Hardware Mode Selection
CE
WE
H
X
L
H
L
L
X
X
L
H
L
H
Notes
1. HSB STORE operation occurs only if an SRAM Write is done since the last nonvolatile cycle. After the STORE (If any) completes, the part goes into standby
mode, inhibiting all operations until HSB rises.
2. The six consecutive addresses must be in the order listed. WE must be high during all six consecutive CE controlled cycles to enable a nonvolatile cycle.
3. IO state assumes OE < V
. Activation of nonvolatile cycles does not depend on state of OE.
IL
Document Number: 001-51026 Rev. **
■
Power up boot firmware routines must rewrite the nvSRAM
into the desired state. While the nvSRAM is shipped in a
preset state, best practice is to again rewrite the nvSRAM
into the desired state as a safeguard against events that
might flip the bit inadvertently (program bugs, incoming
inspection routines, and so on).
■
The Vcap value specified in this data sheet includes a
minimum and a maximum value size. The best practice is to
meet this requirement and not exceed the maximum Vcap
value because the higher inrush currents may reduce the
reliability of the internal pass transistor. Customers who want
to use a larger Vcap value to make sure there is extra store
charge must discuss their Vcap size selection with Cypress.
HSB
A12–A0
H
X
H
X
H
X
L
X
H
0x0000
0x1555
0x0AAA
0x1FFF
0x10F0
0x0F0F
H
0x0000
0x1555
0x0AAA
0x1FFF
0x10F0
0x0F0E
Nonvolatile RECALL
STK12C68-5 (SMD5962-94599)
Mode
IO
Not Selected
Output High Z
Read SRAM
Output Data
Write SRAM
Input Data
Nonvolatile STORE
Output High Z
Read SRAM
Output Data
Read SRAM
Output Data
Read SRAM
Output Data
Read SRAM
Output Data
Read SRAM
Output Data
Nonvolatile STORE
Output High Z
Read SRAM
Output Data
Read SRAM
Output Data
Read SRAM
Output Data
Read SRAM
Output Data
Read SRAM
Output Data
Output High Z
Power
Standby
[3]
Active
Active
[1]
I
CC2
[2, 3]
Active I
CC2
[2, 3]
Active
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