MC68HC08XL36 Datasheet, PDF (56/362 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Resets and Interrupts
Introduction
Resets and interrupts are responses to exceptional events during
program execution. A reset reinitializes the MCU to its startup condition.
An interrupt vectors the program counter to a service routine.
Resets
Effects
External Reset
Internal Reset
MC68HC08XL36
56
A reset returns the MCU to a known startup condition and begins
program execution from a user-defined memory location.
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.
A logic 0 applied to the RST pin for a time, t_IRL, generates an external
reset. An external reset sets the PIN bit in the reset status register.
Sources:
• Power-on reset
• COP
• Low-voltage inhibit
• 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.
Resets and Interrupts
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