7545 datasheet(36/62 Pages) RENESAS

36 / 62 page

Rev.1.06

Mar 07, 2008

Page 36 of 59

REJ03B0140-0106

7545 Group

Power-on Reset Circuit

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

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

In order to use the power-on reset circuit effectively, the time for

the supply voltage to rise from 0 V to 1.8 V must be set to 1 ms

or less.

Voltage Drop Detection Circuit

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

drop in voltage and to reset the microcomputer if the supply

voltage drops below a set value (Typ.1.75 V). When the STP

instruction is executed, the voltage drop detection circuit is

stopped, so that the power dissipation is reduced.

The operation of the voltage drop detection circuit is disabled by

setting “0” to bit 4 of the Function set ROM data (address

FFDA16) of the built-in QzROM.

Note: The emulator MCU “M37545RLSS” is not equipped with

the voltage drop detection circuit.

RESETOUT Output

RESETOUT function is used to output “L” level from RESET

pin when system reset occurs by the power-on reset, the voltage

drop detection circuit or the watchdog timer. Also, the built-in

pull-up transistor is connected to the RESET pin.

Fig. 36 Operation waveform diagram of power-on reset

circuit

Fig. 37 Operation waveform diagram of voltage drop detection circuit

The voltage drop detection circuit detection voltage of this

product is set up lower than the minimum value of the supply

voltage of the recommended operating conditions.

When the supply voltage of a microcomputer falls below to the

minimum value of recommended operating conditions and

regoes up (ex. battery exchange of an application product),

depending on the capacity value of the bypass capacitor added to

the power supply pin, the following case may cause program

failure ;

supply voltage does not fall below to VDET, and its voltage re-

goes up with no reset.

In such a case, please design a system which supply voltage is

once reduced below to VDET and re-goes up after that.

Fig. 38 VCC and VDET

VCC (Note)

1 ms or les s

Power-on

Reset released

Internal reset signal

Reset

state

Note: Keep the value of supply voltage to the minimum value

or more of the recommended operating conditions.

circuit output

wer-on reset

Vcc

Internal reset signal

Reset voltage (Typ:1.75V)

Microcomputer starts operation

after f(XIN) clock is counted 16384 times.

Note: The voltage drop detection circuit does not have

the hysteresis characteristics in the detected voltage.

Vcc

VDET

Reset

Normal operation

No reset

Program failure may occur.

Recommended

operating condition

min. value

Vcc

VDET

Recommended

operating condition

min. value

7545 Datasheet(PDF) 36 Page - Renesas Technology Corp

7545 Datasheet(HTML) 36 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

Datasheet Download

Link URL