Renesas H8 Series Hardware Manual page 490

8-bit single-chip microcomputer

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Table of Contents

Section 14 Power-On Reset and Low-Voltage Detection Circuits (H8/38124 Group Only)

Figure 14.6 shows a usage example for the LVD function employing pins Vref, extD, and extU.

External power

supply voltage

External reference

voltage 1.3 V

Setting conditions:

• Vref = 1.3 V external input (This Vref value results in a Vreset value of 2.5 V.)

• Power supply drop detection voltage input of 2.7 V from extD

• Power supply rise detection voltage input of 2.9 V from extU

• 1 MΩ variable resistor connected externally

Figure 14.6 LVD Function Usage Example Employing Pins Vref, extD, and extU

Below is an explanation of the method for calculating the external resistor values when using the

Vref, extD, and extU pins for input of reference and detection voltages from sources external to

1. First, determine the overall resistance value, R. The current consumed by the resistor is

determined by the value of R. A lower R will result in a greater current flow, and a higher R

will result in a reduced current flow. The value of R is dependent on the configuration of the

system in which the LSI is installed.

2. Determine the power supply drop detection voltage (Vint(D) and the power supply rise

detection voltage (Vint(U).

3. Using a resistance value calculation table like the one shown below, plug in values for R,

Vreset1, Vint(D), and Vint(U) to calculate the values of Vref, R1, R2, and R3.

Rev. 7.00 Mar 10, 2005 page 448 of 652

REJ09B0042-0700

On-chip reference

voltage generator