MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Freescale Semiconductor 97
Chapter 9 Low-Voltage Inhibit (LVI)

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 of the LVI module include:
Programmable LVI reset
Programmable power consumption
Digital filtering of VDD pin level
Selectable LVI trip voltage

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, VLVRX, and remains at or below that level for nine or more consecutive CGMXCLK.
VLVRX and VLVHX are determined by the TRPSEL bit in the LVISCR (see Figure 9-2). LVIPWR and
LVIRST are in the configuration register (CONFIG). See Chapter 5 Configuration Register (CONFIG).
Figure 9-1. LVI Module Block Diagram
LOW VDD
LVIRST
VDD > LVItrip = 0
VDD < LVItrip = 1
LVIOUT
LVIPWR
DETECTOR
VDD
LVI RESET
FROM CONFIG
FROM CONFIG
VDD
DIGITAL FILTER
CPU CLOCK
ANLGTRIP
TRPSEL
FROM LVISCR