MC908GR8CDWE Datasheet, PDF (195/408 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Freescale Semiconductor, Inc.
Monitor ROM (MON)
Functional Description
POR RESET
IS VECTOR
NO
BLANK?
YES
MONITOR MODE
EXECUTE
MONITOR
CODE
NORMAL USER
MODE
POR
NO
TRIGGERED?
YES
Figure 15-2. Low-Voltage Monitor Mode Entry Flowchart
Enter monitor mode with pin configuration shown in Figure 15-1 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 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 PTA1 pin must remain at logic 0 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. Pulling RST low will not exit monitor
mode in this situation.
MC68HC908GR8 — Rev 4.0
MOTOROLA
Monitor ROM (MON)
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Technical Data
195