Renesas H8/38024 Series, Hardware Manual

Page: 465 / 661

Rev. 6.00, 08/04, page 435 of 628
Figure 14.6 shows a usage example for the LVD function employing pins Vref, extD, and extU.
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 M
Ω
variable resistor connected externally
Vref
extU
extD
R1 =
517 k
Ω
R2 =
33 k
Ω
R3 =
450 k
Ω
External reference
voltage 1.3 V
On-chip reference
voltage generator
LVDRES
Interrupt
controller
LVDCR
LVDSR
Interrupt
request
LVDINT
+
−
+
−
On-chip
ladder
resistor
External power
supply voltage
R1
R2
D1
U1
U2
D2
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.