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.
