XC2200 Derivatives
System Units (Vol. 1 of 2)
Memory Organization
User’s Manual
3-42
V2.1, 2008-08
MemoryX2K, V1.3
To summarize:
•
Read protection is always globally affecting the whole flash memory range. Code
fetches and data reads can be separately controlled.
•
Write protection can be global when the read protection is effective or it can be
specific for each logical sector.
The lower and the middle security layers determine how the 4 effective IMB_IMBCTR
fields are preset, changed and how software can access them. This is discussed in the
following paragraphs.
Initialization of the Effective Security Level
After Application Reset protection is activated so that RPA, WPA, DDF and DCF are set.
During startup the IMB Core determines the stored security level as described in
Lower Layer “Physical State”” on Page 3-39
and sets IMB_FSR.PROIN and
IMB_FSR.PROINER and IMB_PROCONx as described in
. The IMB Core further initializes the IMB_IMBCTR fields RPA and
WPA according to the rules of
.
The bits DDF and DCF of the IMB_IMBCTR are not initialized by the IMB Core. During
system startup they are initialized depending on the startup condition. If code fetching
starts in the flash memory then they are set to the inactive state. In all other cases they
are activated to prevent read access to the flash memory without proving password
knowledge.
Changing the Effective Security Level
During run-time the effective security level can be changed. This can be done by directly
writing to the IMB_IMBCTR register or indirectly by changing the bits of the middle layer
by commands as “
” or even double indirectly by changing the
content of the security pages which changes bits in the middle layer and influences the
effective security level.
Writing directly to IMB_IMBCTR:
•
DCF and DDF can be deactivated only if RPA is inactive. They can always be
activated.
Indirectly by using a command sequence:
•
A successful “
” sets RPRODIS and clears RPA.
1 | #
1 | #
Global write protection.
1 | #
0
Sector specific write protection depending on
IMB_PROCONx.
Table 3-6
Effective Write Security
(cont’d)
WPA
RPA
Security Level