mc68hc908mr24 Freescale Semiconductor, Inc, mc68hc908mr24 Datasheet - Page 99

• Manufacturer Part Number: mc68hc908mr24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

7.4.2.2 Computer Operating Properly (COP) Reset
7.4.2.3 Illegal Opcode Reset
7.4.2.4 Illegal Address Reset
MC68HC908MR24 — Rev. 4.1
Freescale Semiconductor
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 bits 12–4 of
the SIM counter. The SIM counter output, which occurs at least every 2
– 2
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
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
RST pin disables the COP module.
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.
Because the MC68HC908MR24 has stop mode disabled, execution of
the STOP instruction will cause an illegal opcode reset.
An opcode fetch from addresses other than FLASH or RAM addresses
generates an illegal address reset (unimplemented locations within
memory map). 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.
4
CGMXCLK cycles, drives the COP counter. The COP should be
System Integration Module (SIM)
System Integration Module (SIM)
Advance Information
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