7549 datasheet(46/86 Pages) RENESAS

46 / 86 page

Rev.2.02

Mar 31, 2009

Page 44 of 81

REJ03B0202-0202

7549 Group

Power-on Reset Circuit

Reset can be automatically performed at power on (power-on

reset) by the built-in power-on reset circuit.

To use the built-in power-on reset circuit, leave the RESET pin

open (the pull-up resistor is built-in).

Low Voltage Detection Circuit

The built-in low voltage detection circuit is designed to detect a

drop in voltage and to reset the microcomputer if the power

source voltage drops below a set value (Typ.1.95 V).

The low voltage detection circuit is valid by setting “1” to bit 0

of the function set ROM data 0.

Also, when “1” is set to bit 2 of the function set ROM data 1, the

low voltage detection circuit can be valid even in the stop mode.

The low voltage detection circuit is stopped in the stop mode by

setting “0” to this bit, so that the power dissipation is reduced.

Fig 56. Operation waveform diagram of power-on

reset circuit

Fig 57. Operation waveform diagram of low voltage detection circuit

Fig 58. Timing diagram at reset

VCC (Note)

Power-on reset circuit output

Internal reset signal

Note: Keep the value of supply voltage to

the minimum value or more of the

recommended operating conditions.

Reset released

Reset

state

Power-on

VCC

Internal reset signal

Reset voltage (Typ:1.95V)

Microcomputer starts operation

by the built-in on-chip oscillator.

FFFC

FFFD

ADH,ADL

ADL

ADH

Reset address from the

vector table

Low-speed on-chip

oscillator clock

Internal CPU clock

RESET

Internal reset

signal

SYNC

Address

Data

9 to 16 cycles of

internal CPU clock

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