M29W128GH70N3E Datasheet, PDF (24/94 Pages) Numonyx B.V – 128-Mbit (16 Mbit x8 or 8 Mbit x16, page, uniform block) 3 V supply flash memory

Software protection
M29W128GH, M29W128GL
5.1
Volatile protection mode
The volatile protection allows the software application to easily protect blocks against
inadvertent change. However, the protection can be easily disabled when changes are
needed. Volatile protection bits, VPBs, are volatile and unique for each block and can be
individually modified. VPBs only control the protection scheme for unprotected blocks that
have their non-volatile protection bits, NVPBs, cleared (erased to ‘1’) (see Section 5.2: Non-
volatile protection mode and Section 6.3.5: Non-volatile protection mode command set).
By issuing the VPB Program or VPB Clear commands, the VPBs are set (programmed to
‘0’) or cleared (erased to ‘1’), thus placing each block in the protected or unprotected state
respectively. The VPBs can be set (programmed to ‘0’) or cleared (erased to ‘1’) as often as
needed.
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:
„ 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 Table 19: Block protection
status)
„ If the option to set the VPBs after power-up is selected, the blocks default to be
protected.
Refer to Section 6.3.7 for a description of the volatile protection mode command set.
5.2
Non-volatile protection mode
5.2.1 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 bit).
If one of the non-volatile protected blocks needs to be unprotected (corresponding NVPB
set to ‘1’), a few more steps are required:
1. First, the NVPB lock bit must be cleared by either putting the device through a power
cycle, or hardware reset
2. The NVPBs can then be changed to reflect the desired settings
3. The NVPB lock bit must be set once again to lock the NVPBs. The device operates
normally again.
Note: 1 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_PP/WP Low, V_IL.
2 The NVPBs and VPBs have the same function when V_PP/WP pin is High, V_IH, as they do
when V_PP /WP pin is at the voltage for program acceleration (V_PPH).
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