4571 datasheet(43/126 Pages) RENESAS

43 / 126 page

Rev.1.02

May 25, 2007

Page 43 of 124

REJ03B0179-0102

4571 Group

(1) Voltage drop detection circuit interrupt request flag

(VDF)

Voltage drop detection circuit interrupt request flag (VDF) is set

to “1” when the supply voltage goes the defined value (VINT) or

less. Moreover, voltage drop detection circuit interrupt request

flag (VDF) is cleared to “0” when the supply voltage goes the

defined value (VINT) or more. The state of the interrupt request

flag can be examined with the skip instruction (SNZVD). Use the

interrupt control register V2 to select an interrupt or a skip

instruction. Unlike other interrupt request flags, even when the

interrupt occurs or the skip instruction is executed, the voltage

drop detection circuit interrupt request flag is not cleared to “0”.

(2) Voltage drop detection circuit reset

System reset is performed when the supply voltage goes the

defined value (VRST-) or less (“L” level is not output to RESET

pin.). However, unlike the normal system reset, the oscillation

circuit is stopped.

When the supply voltage goes the defined value (VRST-) or more,

the oscillation circuit goes to be in the operating enabled state

and system reset is released.

Fig 45. Voltage drop detection circuit operation waveform

Fig 46. VDD and VRST-

(3) Note on voltage drop detection circuit

The voltage drop detection circuit detection voltage of this

product is set up lower than the minimum value of the supply

voltage of the recommended operating conditions.

When the supply voltage of a microcomputer falls below to the

minimum value of recommended operating conditions and rises

again, depending on the capacity value of the bypass capacitor

added to the power supply pin, the following case may cause

program failure (Figure 46);

supply voltage does not fall below to VRST-, and

its voltage rises again with no reset.

In such a case, please design a system which supply voltage is

once reduced below to VRST- and re-goes up after that.

VDD

Voltage drop detection circuit

interrupt request flag (VDF)

VRST+(reset release voltage)

VRST-(reset occurrence voltage)

Voltage drop

detection circuit

reset signal

Notes 1: Microcomputer starts operation after input clock is counted 5400 to 5424 times.

2: “L” level is not output from RESET pin. The oscillation circuit is stopped.

3: After microcomputer starts operation, the detection of the interrupt occurrence voltage is performed.

(Note 1)

(Note 2)

(Note 3)

VINT (interrupt occurrence voltage )

VDD

VRST+

VRST-

VDD

VRST+

VRST-

Recommended operating condition

min.value

Normal operation

Reset

No reset

Program failure may occur.

Recommended operating condition

min.value

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