IBM EM78P447N Power On Considerations, External Power On Reset Circuit, Customer ID Register Word

EM78P447N

8-Bit Microcontroller with OTP ROM

4.8.2 Customer ID Register (Word 1)

Word 1

Bit 12~Bit 0

XXXXXXXXXXXXX

Bit 12~0: Customer’s ID code

4.9 Power On Considerations

Any microcontroller is not guaranteed to start and operate properly before the power supply stays at its steady state. EM78P447N is equipped with Power On Voltage Detector(POVD) with a detecting level is 2.0V. It will work well if Vdd rises fast enough (10 ms or less). In many critical applications, however, extra devices are still required to assist in solving power-up problems.

4.10 External Power On Reset Circuit

The circuit shown in Fig.16 implements an external RC to produce the reset pulse. The pulse width (time constant) should be kept long enough for Vdd to reached minimum operation voltage. This circuit is used when the power supply has slow rise time. Because the current leakage from the /RESET pin is about ±5∝A, it is recommended that R should not be greater than 40 K. In this way, the /RESET pin voltage is held below 0.2V. The diode (D) acts as a short circuit at the moment of power down. The capacitor C will discharge rapidly and fully. Rin, the current-limited resistor, will prevent high current or ESD (electrostatic discharge) from flowing to pin /RESET.

Vdd
/RESET		R
		D
EM78P447N
	Rin	C

Fig. 13 External Power-Up Reset Circuit

28 • Product Specification (V1.1) 03.30.2005

(This specification is subject to change without further notice)