MC68HC08AS32A Datasheet, PDF(141/296 Page) Motorola, Inc – Microcontrollers

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MC68HC08AS32A Datasheet, PDF (141/296 Pages) Motorola, Inc – Microcontrollers

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Freescale Semiconductor, Inc.

Data Sheet â 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 VDD pin and can force a reset when the VDD voltage falls to the LVI

trip voltage.

9.2 Features

Features of the LVI module include:

â¢ Programmable LVI reset

â¢ 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 VDD voltage. The LVI reset bit,

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

voltage, VTRIPF. 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 VDD. 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 VDD rises above a voltage, VTRIPR. 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 VDD levels below the VTRIPF level, software can

monitor VDD 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 VDD to remain above the VTRIPF level, enabling LVI

resets allows the LVI module to reset the MCU when VDD falls to the VTRIPF level.

In the MORA register, the LVIPWR and LVIRST bits must be set to enable the LVI

module and to enable LVI resets.

MC68HC08AS32A â Rev. 1

MOTOROLA

Low-Voltage Inhibit (LVI)

For More Information On This Product,

Go to: www.freescale.com

Data Sheet

141

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