Cypress STK12C68 User Manual
STK12C68
Document Number: 001-51027 Rev. **
Page 6 of 20
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 applications has
resulted in the following suggestions as best practices:
While ease-of-use is one of the product’s main system values,
experience gained working with hundreds of applications 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 should not assume that an NV array
is in a set programmed state. Routines that check memory
content values to determine first time system configuration,
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
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 should not assume that an NV array
is in a set programmed state. Routines that check memory
content values to determine first time system configuration,
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.
consistently.
■
Power up boot firmware routines should 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).
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 should
discuss their Vcap size selection with Cypress.
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 should
discuss their Vcap size selection with Cypress.
Table 1. Hardware Mode Selection
CE
WE
HSB
A12–A0
Mode
IO
Power
H
X
H
X
Not Selected
Output High Z
Standby
L
H
H
X
Read SRAM
Output Data
Active
L
L
H
X
Write SRAM
Input Data
Active
X
X
L
X
Nonvolatile STORE
Output High Z
I
CC2
L
H
H
0x0000
0x1555
0x1555
0x0AAA
0x1FFF
0x10F0
0x0F0F
0x0F0F
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Nonvolatile STORE
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output High Z
Active I
CC2
L
H
H
0x0000
0x1555
0x1555
0x0AAA
0x1FFF
0x10F0
0x0F0E
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Read SRAM
Nonvolatile RECALL
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output Data
Output High Z
Active
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. I/O state assumes OE < V
3. I/O state assumes OE < V
IL
. Activation of nonvolatile cycles does not depend on state of OE.