Cypress CY14B101L manual Preventing Store, Best Practices

CY14B101L

Preventing Store

Disable the AutoStore function by initiating an AutoStore Disable sequence. A sequence of READ operations is performed in a manner similar to the software STORE initiation. To initiate the AutoStore Disable sequence, perform the following sequence of CE 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 0x8B45 AutoStore Disable

Re-enable the AutoStore by initiating an AutoStore Enable sequence. A sequence of READ operations is performed in a manner similar to the software RECALL initiation. To initiate the AutoStore Enable sequence, perform the following sequence of CE 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 0x4B46 AutoStore Enable

If the AutoStore function is disabled or re-enabled, a manual STORE operation (Hardware or Software) is issued to save the AutoStore state through subsequent power down cycles. The part comes from the factory with AutoStore enabled.

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:

■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 reprogram these values. Final NV patterns are typically repeating patterns of AA, 55, 00, FF, A5, or 5A. End product’s firmware should not assume 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.

■Power up boot firmware routines should rewrite the nvSRAM into the desired state. While the nvSRAM is shipped in a preset state, the 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).

■If autostore is firmware disabled, it does not reset to “autostore enabled” on every power down event captured by the nvSRAM. The application firmware should re-enable or re-disable autostore on each reset sequence based on the behavior desired.

■The VCAP value specified in this data sheet includes a minimum and a maximum value size. Best practice is to meet this requirement and not exceed the maximum VCAP value because higher inrush currents may reduce the reliability of the internal pass transistor. Customers that want to use a larger VCAP value to make sure there is extra store charge should discuss their VCAP size selection with Cypress to understand any impact on the Vcap voltage level at the end of a tRECALL period.

Document Number: 001-06400 Rev. *I Page 5 of 18

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