MC908GZ60CFUE Datasheet, PDF (227/352 Pages) Freescale Semiconductor, Inc – Standard features, Features of the CPU08

Reset and System Initialization
OSC1
PORRST
CGMXCLK
4096
CYCLES
32
CYCLES
32
CYCLES
CGMOUT
RST
IAB
$FFFE
$FFFF
Figure 15-7. POR Recovery
15.3.2.3 Illegal Opcode Reset
The SIM decodes signals from the CPU to detect illegal instructions. An illegal instruction sets the ILOP
bit in the SIM reset status register (SRSR) and causes a reset.
If the stop enable bit, STOP, in the CONFIG1 register is 0, the SIM treats the STOP instruction as an
illegal opcode and causes an illegal opcode reset. The SIM actively pulls down the RST pin for all internal
reset sources.
15.3.2.4 Illegal Address Reset
An opcode fetch from an unmapped address generates an illegal address reset. The SIM verifies that the
CPU is fetching an opcode prior to asserting the ILAD bit in the SIM reset status register (SRSR) and
resetting the MCU. A data fetch from an unmapped address does not generate a reset. The SIM actively
pulls down the RST pin for all internal reset sources.
15.3.2.5 Low-Voltage Inhibit (LVI) Reset
The low-voltage inhibit module (LVI) asserts its output to the SIM when the V_DD voltage falls to the V_TRIPF
voltage. The LVI bit in the SIM reset status register (SRSR) is set, and the external reset pin (RST) is
asserted if the LVIPWRD and LVIRSTD bits in the CONFIG1 register are 0. The RST pin will be held low
while the SIM counter counts out 4096 + 32 CGMXCLK cycles after V_DD rises above V_TRIPR. Thirty-two
CGMXCLK cycles later, the CPU is released from reset to allow the reset vector sequence to occur. The
SIM actively pulls down the RST pin for all internal reset sources.
15.3.2.6 Monitor Mode Entry Module Reset (MODRST)
The monitor mode entry module reset (MODRST) asserts its output to the SIM when monitor mode is
entered in the condition where the reset vectors are erased ($FF) (see 20.3.1.1 Normal Monitor Mode).
When MODRST gets asserted, an internal reset occurs. The SIM actively pulls down the RST pin for all
internal reset sources.
MC68HC908GZ60 • MC68HC908GZ48 • MC68HC908GZ32 Data Sheet, Rev. 6
Freescale Semiconductor
227