4524 Datasheet, PDF (78/161 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4524 Group
19 _{A/D converter-2}
Each analog input pin is equipped with a capacitor which is used
to compare the analog voltage. Accordingly, when the analog volt-
age is input from the circuit with high-impedance and, charge/
discharge noise is generated and the sufficient A/D accuracy may
not be obtained. Therefore, reduce the impedance or, connect a
capacitor (0.01 µF to 1 µF) to analog input pins (Figure 72).
When the overvoltage applied to the A/D conversion circuit may
occur, connect an external circuit in order to keep the voltage
within the rated range as shown the Figure 73. In addition, test
the application products sufficiently.
Sensor
AI N
21 _{POF and POF2 instructions}
When the POF or POF2 instruction is executed continuously af-
ter the EPOF instruction, system enters the power down state.
Note that system cannot enter the power down state when ex-
ecuting only the POF or POF2 instruction.
Be sure to disable interrupts by executing the DI instruction be-
fore executing the EPOF instruction and the POF or POF2
instruction continuously.
22 _{Power-on reset}
When the built-in power-on reset circuit is used, the time for the supply
voltage to rise from 0 V to 2.0 V must be set to 100 µs or less. If the ris-
ing time exceeds 100 µs, connect a capacitor between the RESET pin
and VSS at the shortest distance, and input “L” level to RESET pin until
the value of supply voltage reaches the minimum operating voltage.
Apply the voltage withiin the specifications
to an analog input pin.
Fig. 72 Analog input external circuit example-1
Sensor
About 1kΩ
AI N
Fig. 73 Analog input external circuit example-2
20 _{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 re-
goes up (ex. battery exchange of an application product),
depending on the capacity value of the bypass capacitor
added to the power supply pin, the following case may cause
program failure (Figure 74);
supply voltage does not fall below to VRST, and
its voltage re-goes up 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
Recommended
operatng condition
min.value
VRST
No reset
Program failure may occur.
VDD
Recommended
operatng condition
min.value
VRST
Fig. 74 VDD and VRST
Reset
→ Normal operation
23 _{Clock control}
Execute the CMCK or the CRCK instruction in the initial setting routine
of program (executing it in address 0 in page 0 is recommended).
The oscillation circuit by the CMCK or CRCK instruction can be
selected only at once. The oscillation circuit corresponding to the
first executed one of these two instruction is valid. Other oscilla-
tion circuits and the on-chip oscillator stop.
24 On-chip oscillator
The clock frequency of the on-chip oscillator depends on the sup-
ply voltage and the operation temperature range.
Be careful that margin of frequencies when designing application
products.
Also, the oscillation stabilize wait time after system is released from re-
set is generated by the on-chip oscillator clock. When considering the
oscillation stabilize wait time after system is released from reset, be
careful that the margin of frequency of the on-chip oscillator clock.
25 External clock
When the external clock signal is used as the main clock (f(XIN)), note
that the power down mode (POF or POF2 instruction) cannot be used.
26 _{Difference between Mask ROM version and One Time PROM version}
Mask ROM version and One Time PROM version have some dif-
ference of the following characteristics within the limits of an
electrical property by difference of a manufacture process, built-
in ROM, and a layout pattern.
• a characteristic value
• the amount of noise-proof
• a margin of operation
• noise radiation, etc.,
Accordingly, be careful of them when swithcing.
27 _{Note on Power Source Voltage}
When the power source voltage value of a microcomputer is less
than the value which is indicated as the recommended operating
conditions, the microcomputer does not operate normally and
may perform unstable operation.
In a system where the power source voltage drops slowly when
the power source voltage drops or the power supply is turned off,
reset a microcomputer when the supply voltage is less than the
recommended operating conditions and design a system not to
cause errors to the system by this unstable operation.
Rev.2.00 Jul 27, 2004 page 78 of 159
REJ03B0091-0200Z