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7542 Group
Rev.3.02
Oct 31, 2006
Page 58 of 134
REJ03B0006-0302
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.
Fig. 70 Example of reset circuit
Fig. 71 Timing diagram at reset
(Note)
0.2 VCC
0 V
Poweron
VCC
RESET
VCC
RESET
Power source
voltage
detection circuit
Power source
voltage
Reset input
voltage
Note : Reset release voltage Vcc = 2.2 V
Data
Address
8-13 clock cycles
Reset address from the
vector table
1 : An on-chip oscillator applies about RING2 MHz, φ250 kHz frequency clock
at average of Vcc = 5 V.
2 : The mark “?” means that the address is changeable depending on the previous state.
3 : These are all internal signals except RESET.
Notes
??
FFFC
FFFD
ADH,ADL
??
?
??
ADL
ADH
??
?
Clock from
on-chip oscillator
RING
φ
RESET
RESETOUT
SYNC