MC68HC908EY16 Datasheet, PDF (159/278 Pages) Motorola, Inc – Microcontrollers

Reset and System Initialization
OSC1
PORRST
CGMXCLK
4096
CYCLES
32
CYCLES
CGMOUT
RST
IAB
$FFFE
$FFFF
Figure 14-6. POR Recovery
14.3.2.2 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 (SRSR).
To prevent a COP module timeout, write any value to location $FFFF. Writing to location $FFFF clears
the COP counter and stages 12–5 of the SIM counter. The SIM counter output, which occurs at least
every 4080 CGMXCLK cycles, drives the COP counter. The COP should be serviced as soon as possible
out of reset to guarantee the maximum amount of time before the first timeout.
The COP module is disabled if the IRQ pin is held at V_TST while the MCU is in monitor mode. The COP
module can be disabled only through combinational logic conditioned with the high-voltage signal on the
IRQ pin. This prevents the COP from becoming disabled as a result of external noise.
14.3.2.3 Illegal Opcode Reset
The SIM decodes signals from the CPU to detect illegal instructions. An illegal instruction sets the ILOP
bit in the SIM reset status register (SRSR) and causes a reset.
If the stop enable bit, STOP, in the configuration register (CONFIG1) is 0, the SIM treats the STOP
instruction as an illegal opcode and causes an illegal opcode reset.
14.3.2.4 Illegal Address Reset
An opcode fetch from an unmapped address generates an illegal address reset. The SIM verifies that the
CPU is fetching an opcode prior to asserting the ILAD bit in the SIM reset status register (SRSR) and
resetting the MCU. A data fetch from an unmapped address does not generate a reset.
14.3.2.5 Forced Monitor Mode Entry Reset (MENRST)
The MENRST module is monitoring the reset vector fetches and will assert an internal reset if it detects
that the reset vectors are erased ($FF). When the MCU comes out of reset, it is forced into monitor mode.
See 19.3 Monitor Module (MON).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
159