Chapter 9 Security (S12XE9SECV2)
MC9S12XE-Family Reference Manual , Rev. 1.19
346
Freescale Semiconductor
9.1.2
Modes of Operation
gives an overview over availability of security relevant features in unsecure and secure modes.
9.1.3
Securing the Microcontroller
Once the user has programmed the Flash and EEPROM, the chip can be secured by programming the
security bits located in the options/security byte in the Flash memory array. These non-volatile bits will
keep the device secured through reset and power-down.
The options/security byte is located at address 0xFF0F (= global address 0x7F_FF0F) in the Flash memory
array. This byte can be erased and programmed like any other Flash location. Two bits of this byte are used
for security (SEC[1:0]). On devices which have a memory page window, the Flash options/security byte
is also available at address 0xBF0F by selecting page 0x3F with the PPAGE register. The contents of this
byte are copied into the Flash security register (FSEC) during a reset sequence.
The meaning of the bits KEYEN[1:0] is shown in
. Please refer to
the MCU Using the Backdoor Key Access”
for more information.
Table 9-2. Feature Availability in Unsecure and Secure Modes on S12XE
Unsecure Mode
Secure Mode
NS
SS
NX
ES
EX
ST
NS
SS
NX
ES
EX
ST
Flash Array Access
✔
✔
✔
(1)
1. Availability of Flash arrays in the memory map depends on ROMCTL/EROMCTL pins and/or the state of the
ROMON/EROMON bits in the MMCCTL1 register. Please refer to the S12X_MMC block guide for detailed
information.
✔
✔
✔
✔
—
—
—
—
EEPROM Array Access
✔
✔
✔
✔
✔
✔
✔
✔
—
—
—
—
NVM Commands
✔
(2)
2. Restricted NVM command set only. Please refer to the NVM wrapper block guides for detailed information.
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
BDM
✔
✔
✔
✔
✔
✔
—
✔
(3)
3. BDM hardware commands restricted to peripheral registers only.
—
—
—
—
DBG Module Trace
✔
✔
✔
✔
✔
✔
—
—
—
—
—
—
XGATE Debugging
✔
✔
✔
✔
✔
✔
—
—
—
—
—
—
External Bus Interface
—
—
✔
✔
✔
✔
—
—
✔
✔
✔
✔
Internal status visible
multiplexed on
external bus
—
—
—
✔
✔
—
—
—
—
✔
✔
—
Internal accesses visible
on external bus
—
—
—
—
—
✔
—
—
—
—
—
✔
7
6
5
4
3
2
1
0
0xFF0F
KEYEN1
KEYEN0
NV5
NV4
NV3
NV2
SEC1
SEC0
Figure 9-1. Flash Options/Security Byte
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
S12XE
products
in
208
MAPBGA
packages