M28W320 데이터 시트보기 (PDF) - STMicroelectronics
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M28W320 Datasheet PDF : 69 Pages
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M28W320FCT, M28W320FCB
5
Block locking
Block locking
The M28W320FCT and M28W320FCB feature an instant, individual block locking scheme
that allows any block to be locked or unlocked with no latency. This locking scheme has
three levels of protection.
● Lock/Unlock - this first level allows software-only control of block locking.
● Lock-Down - this second level requires hardware interaction before locking can be
changed.
● VPP ≤ VPPLK - the third level offers a complete hardware protection against program
and erase on all blocks.
The protection status of each block can be set to Locked, Unlocked, and Lock-Down.
Table 10 defines all of the possible protection states (WP, DQ1, DQ0), and Appendix C,
Figure 22, shows a flowchart for the locking operations.
5.1
Reading a Block’s Lock Status
The lock status of every block can be read in the Read Electronic Signature mode of the
device. To enter this mode write 90h to the device. Subsequent reads at the address
specified in Table 6, will output the protection status of that block. The lock status is
represented by DQ0 and DQ1. DQ0 indicates the Block Lock/Unlock status and is set by the
Lock command and cleared by the Unlock command. It is also automatically set when
entering Lock-Down. DQ1 indicates the Lock-Down status and is set by the Lock-Down
command. It cannot be cleared by software, only by a hardware reset or power-down.
The following sections explain the operation of the locking system.
5.2
Locked state
The default status of all blocks on power-up or after a hardware reset is Locked (states
(0,0,1) or (1,0,1)). Locked blocks are fully protected from any program or erase. Any
program or erase operations attempted on a locked block will return an error in the Status
Register. The Status of a Locked block can be changed to Unlocked or Lock-Down using the
appropriate software commands. An Unlocked block can be Locked by issuing the Lock
command.
5.3
Unlocked state
Unlocked blocks (states (0,0,0), (1,0,0) (1,1,0)), can be programmed or erased. All unlocked
blocks return to the Locked state after a hardware reset or when the device is powered-
down. The status of an unlocked block can be changed to Locked or Locked-Down using the
appropriate software commands. A locked block can be unlocked by issuing the Unlock
command.
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