EM78P5840/5841/5842
8-bit Micro-controller
(CPU stop)
Sleep
M ode
Reset
ERC orIRC2:ON
IRC1:ON
PLL :turnoff
RESET
operation
run"SLEP"
Reset
Normal
M ode
ERC orIRC2:ON
IRC1:ON
PLL :turnoff
Fig 15: The relative of IRC and ERIC mode’s normal and sleep mode
VII.12 Power on Considerations
Any micro-controller is not guaranteed to start to operate properly before the power supply stabilizes at
its steady states. EM78P5840 power on reset voltage range is 1.6V ~ 2.0V. Under customer application, VDD
must drop to below 1.6V and remains OFF for 10uS before power can be switched on again. This way,
EM78P5840 will reset and work normally. The extra external reset circuit will work well if VDD can rise at very
fast speed (50mS or less). However, under most cases where critical applications are involved, extra devices are
required to assist in solving the power-up problems.
VII.13 External Power on Reset circuit
By Setting code option “P71S” to 1, /RESET pin is selected. Next figure is an external RC to produce the reset
pulse. The pulse width should be kept long enough for VDD to reach minimum operation voltage. The diode D
acts as a short circuit at the moment of power down. The capacitor C will discharged rapidly and fully.
VDD
D
R
C
/RESET
Fig 15: External power on reset circuit 1
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* This specification is subject to change without notice.
36
2004/11/10 V2.6
ELAN [ ELAN MICROELECTRONICS CORP ]
