ST92F124/F150/F250 - SINGLE VOLTAGE FLASH & E3 TM (EMULATED EEPROM)
PROTECTION STRATEGY (Cont’d)
Bit APEX can be temporarily disabled by execut-
ing the Set Protection operation and writing 1 into
NON VOLATILE PASSWORD (NVPWD1-0)
this bit, but only if this write instruction is executed
Address: 231FFF-231FFEh - Write Only
Delivery value: 1111 1111 (FFh)
from an internal memory (Flash and Test Flash ex-
cluded).
Bit APEE can be temporarily disabled by execut-
ing the Set Protection operation and writing 1 into
this bit, but only if this write instruction is executed
from the memory itself to unprotect (E3 TM).
7
6
5
4
3
2
1
0
PWD7 PWD6 PWD5 PWD4 PWD3 PWD2 PWD1 PWD0
Bits APRO and APBR can be temporarily disabled
through a direct write at NVAPR location, by over-
writing at 1 these bits, but only if this write instruc-
tion is executed from the memory itself to unpro-
tect.
Bit 7:0 = PWD[7:0]: Password bits 7:0 (Write On-
ly).
These bits must be programmed with the Non Vol-
atile Password that must be provided with the Set
Protection operation to disable (first write access)
or to reenable (second write access) the test and
EPB modes. The first write access fixes the pass-
word value and resets the TMDIS bit of NVWPR
(231FFDh). The second write access, with Pro-
gram Data matching with NVPWD[1:0] content, re-
sets the PWOK bit of NVWPR.
To restore the access protections, reset the micro
or execute another Set Protection operation by
writing 0 to the desired bits.
Note: To restore all the protections previously en-
abled in the NVAPR or NVWPR register, read the
corresponding register.
When an internal memory (Flash, TestFlash or
These two registers can be accessed only in write
mode (a read access returns FFh).
E
3 TM) is protected in access, also the data access
through a DMA of a peripheral is forbidden (it re-
turns FFh). To read data in DMA mode from a pro-
tected memory, first it is necessary to temporarily
unprotect that memory.
3.5.2 Temporary Unprotection
On user request the memory can be configured so
as to allow the temporary unprotection also of all
access protections bits of NVAPR (write protection
bits of NVWPR are always temporarily unprotecta-
ble).
The temporary unprotection allows also to update
a protected code.
Refer to the following figures to manage the Test/
EPB, Access and Write protection modes.
62/426
9
STMICROELECTRONICS [ ST ]
