Cypress CY14B108L Preventing AutoStore, Data Protection, Noise Considerations, Best Practices

PRELIMINARY CY14B108L, CY14B108N

Preventing AutoStore

The AutoStore function is disabled 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, the following sequence of CE controlled read operations 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 0x8B45 AutoStore Disable

The AutoStore is re-enabled 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, the following sequence of CE controlled read operations 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 0x4B46 AutoStore Enable

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

Data Protection

The CY14B108L/CY14B108N protects data from corruption during low voltage conditions by inhibiting all externally initiated STORE and write operations. The low voltage condition is detected when VCC < VSWITCH. If the CY14B108L/CY14B108N is in a write mode (both CE and WE are LOW) at power up, after a RECALL or STORE, the write is inhibited until the SRAM is enabled after tLZHSB (HSB to output active). This protects against inadvertent writes during power up or brown out conditions.

Noise Considerations

Refer to CY application note AN1064.

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 this nvSRAM product are delivered from Cypress with 0x00 written in all cells. 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 should always program a unique NV pattern (that is, complex 4-byte pattern of 46 E6 49 53 hex or more random bytes) as part of the final system manufac- turing test to ensure these system routines work consistently.

■Power up boot firmware routines should rewrite the nvSRAM into the desired state (for example, autostore enabled). 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 such as program bugs and incoming inspection routines.

■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 the nvSRAM internal algorithm calculates VCAP charge and discharge time based on this max VCAP value. Customers that want to use a larger VCAP value to make sure there is extra store charge and store time 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 #: 001-45523 Rev. *B Page 7 of 24

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