System Integration Module (SIM)
Reset and System Initialization
MC68HC08GP32A MC68HC08GP16A
Data Sheet
MOTOROLA
System Integration Module (SIM)
183
15.3.2.2 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 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 through 5 of the SIM counter.
The SIM counter output, which occurs at least every 213 – 24 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 RST pin or the IRQ pin is held at VTST 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, VTST on the RST pin disables the COP module.
15.3.2.3 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 mask option register is 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.
15.3.2.4 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. The SIM actively pulls down the
RST pin for all internal reset sources.
15.3.2.5 Low-Voltage Inhibit (LVI) Reset
The low-voltage inhibit module (LVI) asserts its output to the SIM when the VDD
voltage falls to the VTRIPF voltage. The LVI bit in the SIM reset status register
(SRSR) is set, and the external reset pin (RST) is held low if the LVIPWRD and
LVIRSTD bits in the mask option register are 0. The RST pin will be held low while
the SIM counter counts out 4096 + 32 CGMXCLK cycles after VDD rises above
VTRIPR. Thirty-two CGMXCLK cycles later, the CPU is released from reset to allow
the reset vector sequence to occur. The SIM actively pulls down the RST pin for all
internal reset sources.