MC68HC908GR16 Datasheet, PDF (145/310 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Data Sheet — MC68HC908GR16
Section 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:
• 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
• Selects CGMXCLK divided by four as the bus clock
13.2.2 External Reset
A logic 0 applied to the RST pin for a time, t_RL, generates an external reset. An
external reset sets the PIN bit in the system integration module (SIM) reset status
register.
13.2.3 Internal Reset
Sources:
• Power-on reset (POR)
• Computer operating properly (COP)
• Low-power reset circuits
• Illegal opcode
• Illegal address
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.
MC68HC908GR16 — Rev. 1.0
MOTOROLA
Resets and Interrupts
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Data Sheet
145