MC68HC908GR8A_07 Datasheet, PDF (162/260 Pages) Freescale Semiconductor, Inc – Microcontrollers

System Integration Module (SIM)
OSC1
PORRST
CGMXCLK
4096
CYCLES
32
CYCLES
32
CYCLES
CGMOUT
RST
IRST
IAB
$FFFE
$FFFF
Figure 14-7. 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 SIM reset status register (SRSR). The SIM actively pulls down
the RST pin for all internal reset sources.
The COP module is disabled if the RST pin or 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 RST or the IRQ pin. This prevents the COP from becoming disabled as a result of
external noise. During a break state, V_TST on the RST pin disables the COP module.
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 CONFIG1 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.
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. The SIM actively
pulls down the RST pin for all internal reset sources.
14.3.2.5 Low-Voltage Inhibit (LVI) Reset
The low-voltage inhibit module (LVI) asserts its output to the SIM when the V_DD voltage falls to the V_TRIPF
voltage. The LVI bit in the SIM reset status register (SRSR) is set, and the external reset pin (RST) is held
MC68HC908GR8A • MC68HC908GR4A Data Sheet, Rev. 5
162
Freescale Semiconductor