MC68HC908GT16_07 Datasheet, PDF (139/292 Pages) Freescale Semiconductor, Inc – Microcontrollers

Resets
13.2.3.3 Low-Voltage Inhibit Reset
A low-voltage inhibit (LVI) reset is an internal reset caused by a drop in the power supply voltage to the
LVI_TRIPF voltage.
An LVI reset:
• Holds the clocks to the CPU and modules inactive for an oscillator stabilization delay of 4096
CGMXCLK cycles after the power supply voltage rises to the LVI_TRIPR voltage
• Drives the RST pin low for as long as V_DD is below the LVI_TRIPR voltage and during the oscillator
stabilization delay
• Releases the RST pin 32 CGMXCLK cycles after the oscillator stabilization delay
• Releases the CPU to begin the reset vector sequence 64 CGMXCLK cycles after the oscillator
stabilization delay
• Sets the LVI bit in the SIM reset status register
13.2.3.4 Illegal Opcode Reset
An illegal opcode reset is an internal reset caused by an opcode that is not in the instruction set. An illegal
opcode reset sets the ILOP bit in the SIM reset status register.
If the stop enable bit, STOP, in the CONFIG1 register is a 0, the STOP instruction causes an illegal
opcode reset.
13.2.3.5 Illegal Address Reset
An illegal address reset is an internal reset caused by opcode fetch from an unmapped address. An illegal
address reset sets the ILAD bit in the SIM reset status register.
A data fetch from an unmapped address does not generate a reset.
13.2.4 SIM Reset Status Register
This read-only register contains flags to show reset sources. All flag bits are automatically cleared
following a read of the register. Reset service can read the SIM reset status register to clear the register
after power-on reset and to determine the source of any subsequent reset.
The register is initialized on power-up as shown with the POR bit set and all other bits cleared. During a
POR or any other internal reset, the RST pin is pulled low. After the pin is released, it will be sampled 32
CGMXCLK cycles later. If the pin is not above a V_IH at that time, then the PIN bit in the SRSR may be set
in addition to whatever other bits are set.
NOTE
Only a read of the SIM reset status register clears all reset flags. After
multiple resets from different sources without reading the register, multiple
flags remain set.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
139