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7542 Group
Reset Circuit
The 7542 group starts operation by the on-chip oscillator after sys-
tem is released from reset.
Accordingly, when the rising of power supply voltage passes 2.2V,
set the reset input voltage to become below 0.2Vcc (0.44V).
Moreover, switch CPU clock to the external oscillator after the ris-
ing of power supply voltage passes the minimum operation
voltage and after an oscillation is stabilized.
Note: The minimum operation voltage is decided by the division
ratio of an external oscillator's frequency and a CPU clock.
Decide on an external oscillator's oscillation stabilizing time
after fully evaluating an oscillator's stabilizing time used.
Clock from
on-chip oscillator
RING
φ
RESET
RESET
OUT
SYNC
Address
Data
Fig. 71 Timing diagram at reset
Rev.3.02
Oct 31, 2006
REJ03B0006-0302
?
?
?
?
?
Notes
1 : An on-chip oscillator applies about RING•2 MHz, φ•250 kHz frequency clock
8-13 clock cycles
2 : The mark "?" means that the address is changeable depending on the previous state.
3 : These are all internal signals except RESET.
Page 58 of 134
RESET
RESET
Fig. 70 Example of reset circuit
?
?
FFFC
FFFD
?
?
?
AD
L
at average of Vcc = 5 V.
Poweron
(Note)
Power source
voltage
V
CC
0 V
Reset input
voltage
0.2 V
0 V
Note : Reset release voltage Vcc = 2.2 V
V
CC
Power source
voltage
detection circuit
AD
H
,AD
L
Reset address from the
AD
vector table
H
CC
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