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Switching Address Mode between 3-byte Addressing and 4-byte Addressing in QSPI Semper Flash - KBA232058

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Switching Address Mode between 3-byte Addressing and 4-byte Addressing in QSPI Semper Flash - KBA232058

Author: YongQ_16           Version: **

Question:

How to switch address mode between 3-byte addressing and 4-byte addressing in QSPI Semper Flash?

Answer:

Semper Flash with QSPI interface supports both 3-byte addressing mode and 4-byte addressing mode. Application software can switch between the two address modes during run-time when necessary.

The ADRBYT bit in the Configuration Register-2 (nonvolatile register bit (CFR2N[7]) and volatile register bit (CFR2V[7])) controls the expected address length for all instructions that require address and is selectable between 3-byte or 4-byte addressing.

The CFR2V[7] bit determines the current flash address mode. Modifying the CFR2N[7] bit will also automatically change the CFR2V[7] bit. While modifying CFR2V[7], CFR2N[7] remains unchanged. During flash power-on initialization, CFR2V[7] is loaded from CFR2N[7].

Reversing either CFR2N[7] or CFR2V[7] can switch the address mode. However, modifying CFR2N[7] is not suggested. Programming nonvolatile register is vulnerable to sudden loss of power and may lead to nonvolatile register corruption. Nonvolatile registers have limited erase/program lifecycles.

Reversing CFR2V[7] in single die device to switch address mode is acceptable, but is not recommended for multiple die devices. For multiple dies flash devices, CFR2V[7] on all the dies need to be the same and have to be modified respectively. In the case of switching from 3-byte addressing to 4-byte addressing, CFR2V on higher dies is not accessible, because it requires 4-byte addressing to access higher dies.

Semper Flash with QSPI interface provides two dedicated commands to switch address modes – Enter 4 Byte Address Mode (B7h) and Exit 4 Byte Address Mode (B8h), which set CFR2V[7] to ‘1’ or ‘0’. These two commands do not require address and are sent to all dies when they are issued.

Enter 4 Byte Address Mode (B7h) and Exit 4 Byte Address Mode (B8h) are suggested to be used to switch flash address mode during run-time.

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‎Dec 21, 2020 10:19 PM
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