MC68HC908JW32_09 Datasheet, PDF (101/232 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Table 7-9. RUN (Run User Program) Command
Description
Operand
Data
Returned
Opcode
Executes PULH and RTI instructions
None
None
$28
Command Sequence
FROM
HOST
Security
RUN
RUN
ECHO
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.
SP
HIGH BYTE OF INDEX REGISTER SP + 1
CONDITION CODE REGISTER
SP + 2
ACCUMULATOR
SP + 3
LOW BYTE OF INDEX REGISTER SP + 4
HIGH BYTE OF PROGRAM COUNTER SP + 5
LOW BYTE OF PROGRAM COUNTER SP + 6
SP + 7
Figure 7-6. Stack Pointer at Monitor Mode Entry
7.4 Security
A security feature discourages unauthorized reading of ROM 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.
NOTE
Do not leave locations $FFF6–$FFFD blank. For security reasons, program
locations $FFF6–$FFFD even if they are not used for vectors.
MC68HC908JW32 Data Sheet, Rev. 6
Freescale Semiconductor
101