MC68HC908LB8_05 Datasheet, PDF (176/234 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

System Integration Module (SIM)
OSC1
PORRST
BUSCLKX4
4096
CYCLES
32
CYCLES
BUSCLKX2
RST
IAB
$FFFE
$FFFF
Figure 17-7. POR Recovery
17.3.2.2 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 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.
17.3.2.3 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.
17.3.2.4 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.
17.3.2.5 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
LVI_TRIPF voltage. The LVI bit in the SIM reset status register (SRSR) is set, and the external reset pin
(RST) is held low while the SIM counter counts out 4096 + 32 BUSCLKX4 cycles. Thirty-two BUSCLKX4
MC68HC908LB8 Data Sheet, Rev. 1
176
Freescale Semiconductor