Datasheet

Resets and Interrupts

Technical Data MC68HC908GR8 — Rev 4.0

62 Resets and Interrupts MOTOROLA

4.3.2 External Reset

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 SIM reset status register.

4.3.3 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.

Figure 4-1. Internal Reset Timing

4.3.3.1 Power-On Reset

A power-on reset is an internal reset caused by a positive transition on

the V

pin. V

at the POR must go completely to 0 V to reset the MCU.

This distinguishes between a reset and a POR. The POR is not a brown-

out detector, low-voltage detector, or glitch detector.

RST PIN

PULLED LOW BY MCU

INTERNAL

32 CYCLES 32 CYCLES

CGMXCLK

RESET

Frees

cale Semiconductor,

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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