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XC2200 Derivatives
System Units (Vol. 1 of 2)
Memory Organization
User’s Manual
3-37
V2.1, 2008-08
MemoryX2K, V1.3
and thus the execution of injected OCDS instructions. In case of start after reset in
internal flash, all flash access operations are controlled by the flash-internal user code
and are therefore allowed, as long as not especially disabled by the user, e.g. before
enabling the debug interface.
Per default, the read protection includes a full (global) flash memory write protection
covering all flash modules. This is necessary to eliminate the possibility to program a
dump routine into the Flash, which reads the whole Flash and writes it out via the
external bus or a serial interface. Program and erase accesses to the flash during active
read protection are only possible, if write protection is separately disabled. Flash write
and read protection can be temporarily disabled, if the user authorizes himself with
correct passwords.
The device also features a sector specific write protection. Software locking of flash
memory sectors is provided to protect code and data. This feature disables both program
and erase operations for all protected sectors. With write protection it is supported to
protect the flash memory or parts of it from unauthorized programming or erase
accesses and to provide virus-proof protection for all sectors.
Read and write protection is installed by specific security configuration words which are
programmed by the user directly into two “Security Pages” (SecP0/1). After any reset,
the security configuration is checked by the command state machine (IMB Core) and
installations are stored (and indicated) in related registers. If any protection is enabled
also the security pages are especially protected.
For authorization of short-term disabling of read protection or/and of write protection a
password checking feature is provided. Only with correct 64-bit password a temporary
unprotected state is taken and the protected command sequences are enabled. If not
finished by the command “
Re-Enable Read/Write Protection
”, the unprotected state is
terminated with the next reset. Password checking is based on four 16-bit keywords
(together 64 bits) which are programmed by the user directly into the “Security Page 0”
(SecP0).
Special support is provided to protect also the protection installation itself against any
stressing or beaming aggressors. The codes of configuration bits are selected, so that
in case of any violation in the flash array, on the read path or in registers the protected
state is taken per default. In registers and security pages, protection control bits are
coded always with two bits, having both codes, “00
B
” and “11
B
” as indication of illegal
and therefore protected state.