MC68HC(7)05H12
—
Rev. 1.0
General Release Specification
MOTOROLA
Resets
67
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General Release Specification — MC68HC(7)05H12
Section 5. Resets
5.1 Contents
5.2
5.3
5.4
5.5
5.6
5.6.1
5.6.2
5.6.3
5.6.4
5.7
5.8
5.8.1
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
External Reset (RESET). . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
Internal Resets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
Power-On Reset (POR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70
Computer Operating Properly Reset (COPR). . . . . . . . . . . . . .70
Resetting the COP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70
COP During WAIT Mode. . . . . . . . . . . . . . . . . . . . . . . . . . .71
COP Watchdog Timer Considerations . . . . . . . . . . . . . . . .71
COP Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
Illegal Address Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
Low Voltage Reset (LVR). . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
LVR Operation in WAIT. . . . . . . . . . . . . . . . . . . . . . . . . . . .73
5.2 Introduction
The MCU can be reset from five sources: one external input and four
internal restart conditions. The RESET pin is an input with a Schmitt
trigger. All the internal peripheral modules will be reset by the internal
reset signal (RST). Refer to
Figure 5-2
for reset timing detail. The
RESET pin contains an internal pullup device.
5.3 External Reset (RESET)
The RESET pin is the only external source of a reset. This pin is
connected to a Schmitt trigger input gate to provide an upper and lower
threshold voltage separated by a minimum amount of hysteresis. This
external reset occurs whenever the RESET pin is pulled below the lower