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EM78P809N
8-Bit Microcontroller
60
• Product Specification (V1.0) 07.26.2005
(This specification is subject to change without further notice)
current leakage from the /RESET pin is about ±5μA, it is recommended that R should
not be greater than 40K. 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.
EM78P809N
/RESET
Vdd
D
R
Rin
C
Fig. 35. External Power-Up Reset Circuit
4.18.2 Residue-Voltage Protection
When battery is replaced, device power (VDD) is taken off but residue-voltage remains.
The residue-voltage may trip below V
DD minimum, but not to zero. This condition may
cause a poor power-on reset. Fig.35 and Fig.36 show how to build the residue-voltage
protection circuit.
EM78P809N
/RESET
Vdd
40K
Q1
1N4684
10K
33K
Vdd
Fig. 36. Residue Voltage Protection Circuit 1