m29dw256g Numonyx, m29dw256g Datasheet - Page 21

• Manufacturer Part Number: m29dw256g
• Description: 256-mbit X16, Multiple Bank, Page, Dual Boot 3 V Supply Flash Memory
• Manufacturer: Numonyx

5.2
5.2.1
Note:
5.2.2
1
2
When the parts are first shipped, or after a power-up or hardware reset, the VPBs can be set
or cleared depending upon the ordering option chosen:
Refer to
Non-volatile protection mode
Non-volatile protection bits
A non-volatile protection bit (NVPB) is assigned to each block.
When a NVPB is set to ‘0’, the associated block is protected, preventing any program or
erase operations in this block.
The NVPB bits are set individually by issuing a NVPB Program command. They are non-
volatile and will remain set through a hardware reset or a power-down/power-up sequence.
The NVPBs cannot be cleared individually, they can only be cleared all at the same time by
issuing a Clear all Non-volatile Protection bits command.
The NVPBs can be protected all at a time by setting a volatile bit, the NVPB lock bit (see
Section 5.2.2: Non-volatile protection bit lock
If one of the non-volatile protected blocks needs to be unprotected (corresponding NVPB
set to ‘1’), a few more steps are required:
1.
2.
3.
To achieve the best protection, it is recommended to execute the NVPB Lock Bit Program
command early in the boot code and to protect the boot code by holding V
The NVPBs and VPBs have the same function when V
when V
Refer to
details on the block protection mechanism, and to
volatile protection mode command set.
Non-volatile protection bit lock bit
The non-volatile protection bit lock bit (NVPB lock bit) is a global volatile bit for all blocks.
When set (programmed to ‘0’), it prevents changing the state of the NVPBs. When cleared
(programmed to ‘1’), the NVPBs can be set and reset using the NVPB Program command
and Clear all NVPBs command, respectively.
There is only one NVPB lock bit per device.
If the option to clear the VPBs after power-up is selected, then the blocks can be
programmed or erased depending on the NVPBs state (see
status)
If the option to set the VPBs after power-up is selected, the blocks default to be
protected.
First, the NVPB lock bit must be cleared by either putting the device through a power
cycle, or hardware reset
The NVPBs can then be changed to reflect the desired settings
The NVPB lock bit must be set once again to lock the NVPBs. The device operates
normally again.
PP
Section 6.4.3
Table 9: Block protection status
/WP pin is at the voltage for program acceleration (V
for a description of the volatile protection mode command set.
and
Figure 5: Software protection scheme
bit).
Section 6.4.4
PP
/WP pin is High, V
PPH
for a description of the non-
Table 9: Block protection
).
PP
IH
/WP Low, V
, as they do
for
21/84
IL
.