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EM78P468N/EM78P468L
8-Bit Microcontroller
Product Specification (V1.5) 02.15.2007
• 33
(This specification is subject to change without further notice)
6.7.1 External Power-on Reset Circuit
This circuit implements an external RC to produce a reset pulse (see Fig. 6-10). The
pulse width (time constant) should be kept long enough to allow VDD to reach minimum
operation voltage. This circuit is used when the power supply rise time is slow.
Because the current leakage from the /RESET pin is
±5μA, it is recommended that R
should not be greater than 40K. In this way, the voltage at Pin /RESET is held below
0.2V. The diode (D) acts as a short circuit at power-down. The capacitor, C, is
discharged rapidly and fully. Rin, the current-limited resistor, prevents high current
discharge or ESD (electrostatic discharge) from flowing into Pin /RESET.
Fig. 6-10 External Power-on Reset Circuit
6.7.2 Residue-Voltage Protection
When battery is replaced, device power (VDD) is disconnected but residue-voltage
remains. The residue-voltage may trips below minimum VDD, but above zero. This
condition may cause poor power on reset. Fig. 6-11 and Fig. 6-12 show how to build a
residue-voltage protection circuit
Fig. 6-11 Residue Voltage Protection Circuit 1
Fig. 6-12 Residue Voltage Protection Circuit 2