HD64F38024HV Datasheet, PDF (466/684 Pages) Renesas Technology Corp – Hardware Manual Renesas 8-Bit Single-Chip Microcomputer H8 Family/H8/300L Super Low Power Series

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
R1 =
517 kΩ
R2 =
33 kΩ
R3 =
450 kΩ
extD
extU
Vref
External reference
voltage 1.3 V
On-chip
ladder
resistor
R1
R2
D1 _D2
U1 _U2
+ LVDRES
−
+ LVDINT
−
Interrupt
controller
On-chip reference
voltage generator
LVDCR
LVDSR
Interrupt
request
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
the LSI.
Procedure:
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. 8.00 Mar. 09, 2010 Page 444 of 658
REJ09B0042-0800