EM78P156N

OTP ROM

0

1

1

Enable

1

0

0

Enable

1

0

1

Enable

1

1

0

Enable

1

1

1

Disable

2. Customer ID Register (Word 1)

Bit 12~Bit 0

XXXXXXXXXXXXX

•Bit 12~0: Customer’s ID code

4.9Power On Considerations

Any microcontroller is not guaranteed to start to operate properly before the power supply stays at its steady state.

EM78156N POR voltage range is 1.2V~1.8V. Under customer application, when power is OFF, Vdd must drop to below 1.2V and remains OFF for 10us before power can be switched ON again. This way, the EM78156E will reset and work normally. The extra external reset circuit will work well if Vdd can rise at very fast speed (50 ms or less). However, under most cases where critical applications are involved, extra devices are required to assist in solving the 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.

This specification is subject to change without prior notice. 31

07.29.2004 (V1.2)