Datasheet

System Integration Module (SIM)
Reset and System Initialization
MC68HC908QY4•MC68HC908QT4•MC68HC908QY2•MC68HC908QT2•MC68HC908QY1•MC68HC908QT1
MOTOROLA System Integration Module (SIM) 83
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Figure 7-7. POR Recovery
7.5.2.2 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 time out, 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
(2
12
– 2
4
) BUSCLKX4 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 time out.
The COP module is disabled during a break interrupt with monitor mode
when BDCOP bit is set in break auxiliary register (BRKAR).
PORRST
OSC1
BUSCLKX4
BUSCLKX2
RST
ADDRESS BUS
4096
CYCLES
32
CYCLES
32
CYCLES
$FFFE $FFFF