MC908JB16DWE Datasheet, PDF (105/332 Pages) Freescale Semiconductor, Inc – Microcontrollers

System Integration Module (SIM)
8.4.2.2 Computer Operating Properly (COP) Reset
An input to the SIM is reserved for the COP reset signal. The overflow of
the COP counter causes an internal reset and sets the COP bit in the
SIM reset status register (SRSR). The SIM actively pulls down the RST
pin for all internal reset sources.
To prevent a COP module timeout, write any value to location $FFFF.
Writing to location $FFFF clears the COP counter and stages 12 through
5 of the SIM counter. The SIM counter output, which occurs at least
every 2¹² – 2⁴ OSCDCLK cycles, drives the COP counter. The COP
should be serviced as soon as possible out of reset to guarantee the
maximum amount of time before the first timeout.
The COP module is disabled if the RST pin or the IRQ pin is held at V_TST
while the MCU is in monitor mode. The COP module can be disabled
only through combinational logic conditioned with the high voltage signal
on the RST or the IRQ pin. This prevents the COP from becoming
disabled as a result of external noise. During a break state, V_TST on the
RST pin disables the COP module.
8.4.2.3 Illegal Opcode Reset
The SIM decodes signals from the CPU to detect illegal instructions. An
illegal instruction sets the ILOP bit in the SIM reset status register
(SRSR) and causes a reset.
If the stop enable bit, STOP, in the mask option register is logic 0, the
SIM treats the STOP instruction as an illegal opcode and causes an
illegal opcode reset. The SIM actively pulls down the RST pin for all
internal reset sources.
8.4.2.4 Illegal Address Reset
An opcode fetch from an unmapped address generates an illegal
address reset. The SIM verifies that the CPU is fetching an opcode prior
to asserting the ILAD bit in the SIM reset status register (SRSR) and
resetting the MCU. A data fetch from an unmapped address does not
generate a reset. The SIM actively pulls down the RST pin for all internal
reset sources.
MC68HC908JB16 — Rev. 1.1
Freescale Semiconductor
System Integration Module (SIM)
Technical Data
105