Power Up/Down Requirement in Serial NOR Flash Devices – KBA220676

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What Happens if the Chip Select does not follow VCC in a serial NOR device?



Answer: In Cypress serial NOR devices during power up/down, the Chip Select pin (CS#) must follow VCC as mentioned in respective datasheets. In the case of noncompliance, device initialization can fail. Device initialization involves loading internal device settings, default register values, and so on. An incorrect device initialization can cause the device to respond incorrectly to flash commands.


Here are the possible workarounds for the above scenario:

  • Add a pull-up resistor (generally of the order of 100 kΏ) on Chip Select (CS#) to ensure correct power-up and power-down.
  • Modify the boot software to issue a software reset command before flash detection. The software reset re-initializes the device.