MC68HC908GT16 Datasheet, PDF (216/412 Pages) Motorola, Inc – Microcontrollers

Monitor ROM (MON)
Enter monitor mode with pin configuration shown in Figure 15-3 by
pulling RST low and then high. The rising edge of RST latches monitor
mode. Once monitor mode is latched, the values on the specified pins
can change.
Once out of reset, the MCU waits for the host to send eight security bytes
(see 15.5 Security). After the security bytes, the MCU sends a break
signal (10 consecutive logic 0s) to the host, indicating that it is ready to
receive a command.
NOTE: The PTA0 pin must remain at logic 1 for 24 bus cycles after the RST pin
goes high to enter monitor mode properly.
In monitor mode, the MCU uses different vectors for reset, SWI
(software interrupt), and break interrupt than those for user mode. The
alternate vectors are in the $FE page instead of the $FF page and allow
code execution from the internal monitor firmware instead of user code.
NOTE:
Exiting monitor mode after it has been initiated by having a blank reset
vector requires a power-on reset (POR). Pulling RST low will not exit
monitor mode in this situation.
Table 15-2 summarizes the differences between user mode and monitor
mode.
Modes
User
Monitor
Table 15-2. Mode Differences
Reset
Vector
High
$FFFE
$FEFE
Reset
Vector
Low
$FFFF
$FEFF
Functions
Break
Vector
High
Break
Vector
Low
$FFFC $FFFD
$FEFC $FEFD
SWI
Vector
High
$FFFC
$FEFC
SWI
Vector
Low
$FFFD
$FEFD
Technical Data
216
MC68HC908GT16 • MC68HC908GT8 — Rev. 2
Monitor ROM (MON)
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