EM78P156N Datasheet, PDF (31/58 Pages) ELAN Microelectronics Corp – 8-BIT MICRO-CONTROLLER

EM78P156N
OTP ROM
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2. Customer ID Register (Word 1)
Bit 12~Bit 0
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• Bit 12~0: Customer’s ID code
4.9 Power 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 ±5µA, 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)