Advance Information MC68HC908MR16/MC68HC908MR32 — Rev. 4.0
190 Monitor ROM (MON) MOTOROLA
Monitor ROM (MON)
Enter monitor mode by either:
Executing a software interrupt instruction (SWI) or
Applying a logic 0 and then a logic 1 to the RST pin
Once out of reset, the MCU waits for the host to send eight security
bytes. After receiving the security bytes, the MCU sends a break signal
(10 consecutive logic 0s) to the host computer, indicating that it is ready
to receive a command. The break signal also provides a timing refere nce
to allow the host to determine the necessary baud rate.
Monitor mode uses alternate vectors for reset and SWI. The alternate
vectors are in the $FE page instead of the $FF page and allow code
execution from the internal monitor firmware instead of user code. The
computer operating properly (COP) module is d isabled in mon itor mode
as long as VHI is applied to either the IRQ pin or the RST pin. (See
Section 7. System Integration Module (SIM) for more information on
modes of operation.)
10.4.1.2 Forced Monitor Mode
If the voltage applied to the IRQ1 is less than VDD + VHI the MCU will
come out of reset in user mode. The MENRST modul e is moni toring th e
reset vector fetches and will assert an internal reset if it detects that the
reset vectors are erased ($FF). When the MCU comes out of reset, it is
forced into monitor mode without requiring high vol tage on the IRQ1 pin.
The COP module is disabled in forced monitor mode. Any reset other
than a POR reset will automatically force the MCU to come back to the
forced monitor mode.