4571 Datasheet, PDF (43/126 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

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.
VDD
VINT (interrupt occurrence voltage)
VRST+(reset release voltage)
VRST^-(reset occurrence voltage)
Voltage drop detection circuit
interrupt request flag (VDF)
(Note 3)
Voltage drop
detection circuit
reset signal
(Note 2)
(Note 1)
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.
Fig 45. Voltage drop detection circuit operation waveform
VDD
Recommended operating condition
min.value
VRST+
VRST^-
VDD
Recommended operating condition
min.value
VRST+
VRST^-
Fig 46. VDD and VRST^-
No reset
Program failure may occur.
Normal operation
Reset
(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.
Rev.1.02 May 25, 2007 Page 43 of 124
REJ03B0179-0102