MC68HC08AZ32A Datasheet, PDF(105/312 Page) Motorola, Inc – HCMOS Microcontroller Unit

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MC68HC08AZ32A Datasheet, PDF (105/312 Pages) Motorola, Inc – HCMOS Microcontroller Unit

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Chapter 9

Low-Voltage Inhibit (LVI) Module)

9.1 Introduction

This section describes the low-voltage inhibit (LVI) module, 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 include:

â¢ Programmable LVI reset

â¢ Programmable power consumption

â¢ Digital filtering of VDD pin level

NOTE

If a low-voltage interrupt (LVI) occurs during programming of EEPROM

memory, then adequate programming time may not have been allowed to

ensure the integrity and retention of the data. It is the responsibility of the

user to ensure that in the event of an LVI any addresses being programmed

receive specification programming conditions.

9.3 Functional Description

Figure 9-1 shows the structure of the LVI module. 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, LVITRIPF, and

remains at or below that level for nine or more consecutive CPU cycles.

NOTE

Note that short VDD spikes may not trip the LVI. It is the userâs responsibility

to ensure a clean VDD signal within the specified operating voltage range if

normal microcontroller operation is to be guaranteed.

LVISTOP enables the LVI module during stop mode. This will ensure when the STOP instruction is

implemented the LVI will continue to monitor the voltage level on VDD.

LVIPWR, LVIRST, and LVISTOP are mask options (see Chapter 10 Mask Options). Once an LVI reset

occurs, the MCU remains in reset until VDD rises above a voltage, LVITRIPR. VDD must be above LVITRIPR

for only one CPU cycle to bring the MCU out of reset. 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.

MC68HC08AZ32A Data Sheet, Rev. 2

Freescale Semiconductor

105

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