MC68HC908GT16 Datasheet, PDF(204/412 Page) Motorola, Inc – Microcontrollers

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MC68HC908GT16 Datasheet, PDF (204/412 Pages) Motorola, Inc – Microcontrollers

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Low-Voltage Inhibit (LVI)

14.3 Features

Features of the LVI module include:

â¢ Programmable LVI reset

â¢ Selectable LVI trip voltage

â¢ Programmable stop mode operation

14.4 Functional Description

Figure 14-1 shows the structure of the LVI module. The LVI is enabled

out of reset. The LVI module contains a bandgap reference circuit and

comparator. Clearing the LVI power disable bit, LVIPWRD, enables the

LVI to monitor VDD voltage. Clearing the LVI reset disable bit, LVIRSTD,

enables the LVI module to generate a reset when VDD falls below a

voltage, VTRIPF. Setting the LVI enable in stop mode 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, VTRIPF, to be

configured for 5-V operation. Clearing the LVI5OR3 bit enables the trip

point voltage, VTRIPF, to be configured for 3-V operation. The actual trip

points are shown in Section 23. Electrical Specifications.

NOTE:

After a power-on reset (POR) the LVIâs 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 VDD supply is below the 5-V mode trip voltage but above

the 3-V mode trip voltage when POR is released, the part will operate

because VTRIPF defaults to 3-V mode after a POR. So, in a 5-V system

care must be taken to ensure that VDD is above the 5-V mode trip voltage

after POR is released.

NOTE:

If the user requires 5-V mode and sets the LVI5OR3 bit after a power-on

reset while the VDD supply is not above the VTRIPR for 5-V mode, the

microcontroller unit (MCU) will immediately go into reset. The LVI in this

case will hold the part in reset until either VDD goes above the rising 5-V

trip point, VTRIPR, which will release reset or VDD decreases to

Technical Data

204

MC68HC908GT16 â¢ MC68HC908GT8 â Rev. 2

Low-Voltage Inhibit (LVI)

MOTOROLA

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