MC68HC08AS32A — Rev. 1
Data Sheet
MOTOROLA
Low-Voltage Inhibit (LVI)
141
Data Sheet — MC68HC08AS32A
Section 9. Low-Voltage Inhibit (LVI)
9.1 Introduction
This section describes the low-voltage inhibit module (LVI), which monitors the
voltage on the V
DD
pin and can force a reset when the V
DD
voltage falls to the LVI
trip voltage.
9.2 Features
Features of the LVI module include:
Programmable LVI reset
Programmable power consumption
9.3 Functional Description
Figure 9-1
shows the structure of the LVI module. The LVI is enabled out of reset.
The LVI module contains a bandgap reference circuit and comparator. The LVI
power bit, LVIPWR, enables the LVI to monitor V
DD
voltage. The LVI reset bit,
LVIRST, enables the LVI module to generate a reset when V
DD
falls below a
voltage, V
TRIPF
. LVISTOP, enables the LVI module during stop mode. This will
ensure that when the STOP instruction is executed, the LVI will continue to monitor
the voltage level on V
DD
. LVIPWR, LVISTOP, and LVIRST are in the MORA
register ($001F) (see
Section 10. Mask Options
). Once an LVI reset occurs, the
MCU remains in reset until V
DD
rises above a voltage, V
TRIPR
. The output of the
comparator controls the state of the LVIOUT flag in the LVI status register (LVISR).
An LVI reset also drives the RST pin low to provide low-voltage protection to
external peripheral devices.
9.3.1 Polled LVI Operation
In applications that can operate at V
DD
levels below the V
TRIPF
level, software can
monitor V
DD
by polling the LVIOUT bit. In the MORA register, the LVIPWR bit must
be set to enable the LVI module, and the LVIRST bit must be cleared to disable LVI
resets.
9.3.2 Forced Reset Operation
In applications that require V
DD
to remain above the V
TRIPF
level, enabling LVI
resets allows the LVI module to reset the MCU when V
DD
falls to the V
TRIPF
level.
In the MORA register, the LVIPWR and LVIRST bits must be set to enable the LVI
module and to enable LVI resets.
F
Freescale Semiconductor, Inc.
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.