JS48F4400PCZ00 datasheet(71/102 Pages) NUMONYX

71 / 102 page

November 2007

Datasheet

Order Number: 290701-18

Numonyx™ Wireless Flash Memory (W18)

13.0

Security Modes

The Numonyx Wireless Flash Memory (W18) offers both hardware and software

security features to protect the flash data. The software security feature is used by

executing the Lock Block command. The hardware security feature is used by executing

the Lock-Down Block command and by asserting the WP# signal.

Refer to Figure 31, “Block Locking State Diagram” on page 72 for a state diagram of

the flash security features. Also see Figure 32, “Locking Operations Flowchart” on

page 74.

13.1

Block Lock Operations

Individual instant block locking protects code and data by allowing any block to be

locked or unlocked with no latency. This locking scheme offers two levels of protection.

The first allows software-only control of block locking (useful for frequently changed

data blocks), while the second requires hardware interaction before locking can be

changed (protects infrequently changed code blocks).

The following sections discuss the locking system operation. The term “state [abc]”

specifies locking states; for example, “state [001],” where a = WP# value, b = block

lock-down status bit

D1, and c = Block Lock Status Register bit D0. Figure 31, “Block Locking State

Diagram” on page 72 defines possible locking states.

The following summarizes the locking functionality.

• All blocks power-up in a locked state.

• Unlock commands can unlock these blocks, and lock commands can lock them

again.

• The Lock-Down command locks a block and prevents it from being unlocked when

WP# is asserted.

— Locked-down blocks can be unlocked or locked with commands as long as WP#

is deasserted.

— The lock-down status bit is cleared only when the device is reset or powered-

down.

Block lock registers are not affected by the VPP level. They may be modified and read

even if VPP ≤ VPPLK.

Each block’s locking status can be set to locked, unlocked, and lock-down, as described

in the following sections. See Figure 32, “Locking Operations Flowchart” on page 74.

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