M28C16 데이터 시트보기 (PDF) - STMicroelectronics
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M28C16 Datasheet PDF : 18 Pages
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Figure 5. Software Data Protection Enable Algorithm and Memory Write
Page
Write
Instruction
(Note 1)
WRITE AAh in
Address 555h
WRITE 55h in
Address 2AAh
WRITE A0h in
Address 555h
SDP is set
Page
Write
Instruction
(Note 1)
WRITE AAh in
Address 555h
WRITE 55h in
Address 2AAh
WRITE A0h in
Address 555h
Write Page
(1 up to 64 bytes)
M28C16
WRITE
is enabled
SDP ENABLE ALGORITHM
WRITE IN MEMORY
WHEN SDP IS SET
AI01509B
Note: 1. MSB Address bits (A6 to A10) differ during these specific Page Write operations.
Figure 6. Software Data Protection Disable
Algorithm
Page
Write
Instruction
WRITE AAh in
Address 555h
WRITE 55h in
Address 2AAh
WRITE 80h in
Address 555h
WRITE AAh in
Address 555h
WRITE 55h in
Address 2AAh
WRITE 20h in
Address 555h
Unprotected State
AI01510
Software Data Protection
The M28C16 offers a software controlled write
protection facility that allows the user to inhibit all
write modes to the device including the Chip Erase
instruction. This can be useful in protecting the
memory from inadvertent write cycles that may
occur due to uncontrolled bus conditions.
The M28C16 is shipped as standard in the ”unpro-
tected” state meaning that the memory contents
can be changed as required by the user. After the
Software Data Protection enable algorithm is is-
sued, the device enters the ”Protect Mode” of
operation where no further write commands have
any effect on the memory contents. The device
remains in this mode until a valid Software Data
Protection (SDP) disable sequence is received
whereby the device reverts to its ”unprotected”
state. The Software Data Protection is fully non-
volatile and is not changed by power on/off se-
quences.
To enable the Software Data Protection (SDP) the
device requires the user to write (with a Page Write)
three specific data bytes to three specific memory
locations as per Figure 5. Similarly to disable the
Software Data Protection the user has to write
specific data bytes into six different locations as per
Figure 6 (with a Page Write). This complex series
ensures that the user will never enable or disable
the Software Data Protection accidentally.
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