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TC1796
System Units (Vol. 1 of 2)
Program Memory Unit
User’s Manual
7-33
V2.0, 2007-07
PMU, V2.0
With a reset operation, the FCON register bits DCF and DDF are set. When starting code
execution from internal PFLASH, these flags become cleared by the Boot ROM program
before Boot ROM exit. This means that code execution from PFLASH and data read
accesses from PFLASH or DFLASH is generally allowed. The program code, which
executes the data read accesses from Flash, can be located in any program memory.
When starting from internal or external program RAM (case 2 and 3), flags DCF and DDF
remain set at Boot ROM exit. This means, that code execution from PFLASH and data
read access from PFLASH or DFLASH is disabled. In this case, code or data accesses
from PFLASH or DFLASH are only possible while read protection is temporarily disabled
by the password protected Disable Read Protection command (FCON.RPA is cleared).
In this disable state, it is also possible to clear the DCF/DDF flags of register FCON.
Flash data accesses from dedicated bus masters others than the CPU/DMI can be
disabled separately with FCON register bits DDFDBG, DDFDMA, and DDFPCP of
register FCON. When such a bit is set, the corresponding bus master (Debug system,
DMA controller, or PCP) is not allowed to access PFLASH or DFLASH memory. When
these bits are set once, they can only be cleared again when read protection is not
selected at all (inactive), or temporarily disabled.
Note: The debug interface is disabled after Boot ROM exit with read protection.
7.2.7.4
Password Check Control
The Disable Write Protection command and the Disable Read Protection command
provide a protected command sequence, meaning that two 32-bit passwords must be
issued within the command. Both commands are executed only if the two passwords are
identical with the two keywords that are stored in the corresponding user configuration
block. If one or both passwords are not identical to their related keywords, the protected
sectors remain in the locked state (read- and/or write-protected) and the protection error
flag FSR.PROER is set. In this case, a new Disable Write Protection command or a
Disable Read Protection command is only accepted after the next TC1796 reset
operation.
Note that the Disable Write Protection command can be applied for user 0 (UCB0) or
user 1 (UCB1). The Disable Read Protection command can be applied only for user 0
(UCB0).