UPD64 datasheet(27/68 Pages) NEC

27 / 68 page

µPD63, 63A, 64

7. POC CIRCUIT (MASK OPTION)

The POC circuit monitors the power supply voltage and applies an internal reset in the microcontroller at the

time of battery replacement.

If the applied circuit satisfies the following conditions, the POC circuit can be

incorporated by the mask option.

• High reliability is not required.

• Clock frequency fX =2.4 to 4 MHz

• Power supply voltage VDD = 2.2 to 3.6 V

• Operating ambient temperature TA = –20 to +70 ˚C

Cautions 1. The one-time PROM product (

µPD6P4B) originally contains the POC circuit.

2. There are cases in which the POC circuit cannot detect a low power supply voltage of less

than 1 ms. Therefore, if the power supply voltage has become low for a period of less than

1 ms, the POC circuit may malfunction because it does not generate an internal reset signal.

3. Clock oscillation is stopped by the resonator due to low power supply voltage before the

POC circuit generates the internal reset signal. In this case, malfunction may result, for

example when the power supply voltage is recovered after the oscillation is stopped. This

type of phenomenon takes place because the POC circuit does not generate an internal reset

signal (because the power supply voltage recovers before the low power supply voltage is

detected) even though the clock has stopped. If, by any chance, a malfunction has taken

place, remove the battery for a short time and put it back. In most cases, normal operation

will be resumed.

4. If the applied circuit does not satisfy the conditions above, design the applied circuit in such

a manner that the reset takes effect without failure within the power supply voltage range

by means of an external reset circuit.

5. In order to prevent malfunction, be sure to input a low level to more than one of pins KI0 to

KI3 when reset is released (when RESET pin changes from low level to high level, or POC

is released due to supply voltage startup).

Remarks 1. It is recommended that the POC circuit be incorporated when applied circuits are infrared remote-

control transmitters for household appliances.

2. Even when a POC circuit is incorporated, the externally entered RESET input is valid with the OR

condition; therefore, the POC circuit and the RESET input can be used at the same time. However,

if the POC circuit detects a low power supply voltage, the RESET pin will be forced to low level;

therefore, use an N-ch open drain output or NPN open collector output for the external reset circuit.

UPD64 датащи(PDF) 27 Page - NEC