mc68hc908rc24d Freescale Semiconductor, Inc, mc68hc908rc24d Datasheet - Page 183

• Manufacturer Part Number: mc68hc908rc24d
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

17.5 Security
MC68HC908RC24 — Rev. 1.1
Freescale Semiconductor
NOTE:
The MCU executes the SWI and PSHH instructions when it enters
monitor mode. The RUN command tells the MCU to execute the PULH
and RTI instructions. Before sending the RUN command, the host can
modify the stacked CPU registers to prepare to run the host program.
The READSP command returns the incremented stack pointer value,
SP + 1. The high and low bytes of the program counter are at addresses
SP + 5 and SP + 6.
A security feature discourages unauthorized reading of ROM and
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.
Do not leave locations $FFF6–$FFFD blank. For security reasons,
program locations $FFF6–$FFFD even if they are not used for vectors.
During monitor mode entry, the MCU waits after the power-on reset for
the host to send the eight security bytes on pin PA0.
Figure 17-6. Stack Pointer at Monitor Mode Entry
Monitor ROM (MON)
HIGH BYTE OF PROGRAM COUNTER
LOW BYTE OF PROGRAM COUNTER
HIGH BYTE OF INDEX REGISTER
LOW BYTE OF INDEX REGISTER
CONDITION CODE REGISTER
ACCUMULATOR
SP
SP + 1
SP + 2
SP + 3
SP + 4
SP + 5
SP + 6
SP + 7
Monitor ROM (MON)
Advance Information
Security
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