MC68HC908JB8 Datasheet, PDF (101/286 Pages) Motorola, Inc – MICROCONTROLLERS

System Integration Module (SIM)
Reset and System Initialization
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
reset status register (RSR). 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 OSCXCLK 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_DD + V_HI 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_DD + V_HI 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 reset status register (RSR) 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 reset status register (RSR) 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.
MC68HC908JB8•MC68HC08JB8•MC68HC08JT8 — Rev. 2.3
Freescale Semiconductor
System Integration Module (SIM)
Technical Data
101