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Switching Address Mode between 3-byte Addressing and 4-byte Addressing in QSPI Semper Flash - KBA232058
Author: YongQ_16 Version: **
How to switch address mode between 3-byte addressing and 4-byte addressing in QSPI Semper™ Flash?
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) and volatile register bit (CFR2V)) controls the expected address length for all instructions that require address and is selectable between 3-byte or 4-byte addressing.
The CFR2V bit determines the current flash address mode. Modifying the CFR2N bit will also automatically change the CFR2V bit. While modifying CFR2V, CFR2N remains unchanged. During flash power-on initialization, CFR2V is loaded from CFR2N.
Reversing either CFR2N or CFR2V can switch the address mode. However, modifying CFR2N 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 in single die device to switch address mode is acceptable, but is not recommended for multiple die devices. For multiple dies flash devices, CFR2V 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 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.