mc68hc908gr8a Freescale Semiconductor, Inc, mc68hc908gr8a Datasheet - Page 111

• Manufacturer Part Number: mc68hc908gr8a
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 11
Low-Voltage Inhibit (LVI)
11.1 Introduction
This section describes the low-voltage inhibit (LVI) module, which monitors the voltage on the V
and can force a reset when the V
11.2 Features
Features of the LVI module include:
11.3 Functional Description
Figure 11-1
contains a bandgap reference circuit and comparator. Clearing the LVI power disable bit, LVIPWRD,
enables the LVI to monitor V
module to generate a reset when V
bit, LVISTOP, enables the LVI to operate in stop mode. Setting the LVI 5-V or 3-V trip point bit, LVI5OR3,
enables the trip point voltage, V
enables the trip point voltage, V
in
Freescale Semiconductor
Chapter 19 Electrical
•
•
•
Programmable LVI reset
Selectable LVI trip voltage
Programmable stop mode operation
shows the structure of the LVI module. The LVI is enabled out of reset. The LVI module
After a power-on reset (POR) the LVI’s default mode of operation is 3 V. If
a 5-V system is used, the user must set the LVI5OR3 bit to raise the trip
point to 5-V operation. Note that this must be done after every power-on
reset since the default will revert back to 3-V mode after each power-on
reset. If the V
3-V mode trip voltage when POR is released, the part will operate because
V
taken to ensure that V
released.
If the user requires 5-V mode and sets the LVI5OR3 bit after a power-on
reset while the V
microcontroller unit (MCU) will immediately go into reset. The LVI in this
case will hold the part in reset until either V
point, V
0 V which will re-trigger the power-on reset and reset the trip point to 3-V
operation.
TRIPF
defaults to 3-V mode after a POR. So, in a 5-V system care must be
TRIPR
Specifications.
MC68HC908GR8A • MC68HC908GR4A Data Sheet, Rev. 5
, which will release reset or V
DD
DD
TRIPF
supply is below the 5-V mode trip voltage but above the
DD
TRIPF
voltage. Clearing the LVI reset disable bit, LVIRSTD, enables the LVI
DD
supply is not above the V
DD
, to be configured for 3-V operation. The actual trip points are shown
voltage falls below the LVI trip falling voltage, V
, to be configured for 5-V operation. Clearing the LVI5OR3 bit
DD
falls below a voltage, V
is above the 5-V mode trip voltage after POR is
NOTE
DD
DD
goes above the rising 5-V trip
TRIPR
decreases to approximately
TRIPF
for 5-V mode, the
. Setting the LVI enable in stop mode
TRIPF
.
DD
pin
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