mc68hc908gr16 Freescale Semiconductor, Inc, mc68hc908gr16 Datasheet - Page 135

• Manufacturer Part Number: mc68hc908gr16
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 13
Resets and Interrupts
13.1 Introduction
Resets and interrupts are responses to exceptional events during program execution. A reset re-initializes
the microcontroller (MCU) to its startup condition. An interrupt vectors the program counter to a service
routine.
13.2 Resets
A reset immediately returns the MCU to a known startup condition and begins program execution from a
user-defined memory location.
13.2.1 Effects
A reset:
13.2.2 External Reset
A 0 applied to the RST pin for a time, t
in the system integration module (SIM) reset status register.
13.2.3 Internal Reset
Sources:
All internal reset sources pull the RST pin low for 32 CGMXCLK cycles to allow resetting of external
devices. The MCU is held in reset for an additional 32 CGMXCLK cycles after releasing the RST pin.
13.2.3.1 Power-On Reset (POR)
A power-on reset (POR) is an internal reset caused by a positive transition on the V
POR must go below V
not a brown-out detector, low-voltage detector, or glitch detector.
Freescale Semiconductor
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Immediately stops the operation of the instruction being executed
Initializes certain control and status bits
Loads the program counter with a user-defined reset vector address from locations $FFFE and
$FFFF, $FEFE and $FEFF in monitor mode
Selects CGMXCLK divided by four as the bus clock
Power-on reset (POR)
Computer operating properly (COP)
Low-power reset circuits
Illegal opcode
Illegal address
POR
to reset the MCU. This distinguishes between a reset and a POR. The POR is
MC68HC908GR16 Data Sheet, Rev. 5.0
RL
, generates an external reset. An external reset sets the PIN bit
DD
pin. V
DD
at the
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