mc908jl16 Freescale Semiconductor, Inc, mc908jl16 Datasheet - Page 191

• Manufacturer Part Number: mc908jl16
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

16.3.8 Security
A security feature discourages unauthorized reading of FLASH locations while in monitor mode. The host
can bypass the security feature at monitor mode entry by sending eight security bytes that match the
bytes at locations $FFF6–$FFFD. Locations $FFF6–$FFFD contain user-defined data.
During monitor mode entry, the MCU waits after the power-on reset for the host to send the eight security
bytes on pin PTB0. If the received bytes match those at locations $FFF6–$FFFD, the host bypasses the
security feature and can read all FLASH locations and execute code from FLASH. Security remains
bypassed until a power-on reset occurs. If the reset was not a power-on reset, security remains bypassed
and security code entry is not required. (See
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Command Sequence
Command Sequence
SENT TO
MONITOR
SENT TO
MONITOR
ECHO
ECHO
Data Returned
Data Returned
Description
Description
Operand
Operand
Opcode
Opcode
READSP
RUN
Do not leave locations $FFF6–$FFFD blank. For security reasons, program
locations $FFF6–$FFFD even if they are not used for vectors.
Improved security function denies monitor mode entry if five or more of the
eight security bytes are $00 (zero bytes).
Reads stack pointer
None
Returns stack pointer in high byte:low byte order
$0C
Executes RTI instruction
None
None
$28
READSP
Table 16-8. READSP (Read Stack Pointer) Command
RUN
Table 16-9. RUN (Run User Program) Command
SP HIGH
MC68HC908JL16 Data Sheet, Rev. 1.1
Figure
SP LOW
NOTE
NOTE
16-14.)
RESULT
Monitor Module (MON)
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