PCA84C441 datasheet(8/40 Pages) PHILIPS

8 / 40 page

1996 Nov 29

Philips Semiconductors

Product speciﬁcation

8-bit microcontrollers with OSD and VST

84C44X; 84C64X; 84C84X

RESET

The RESET pin (active LOW input) is used to initialize the

microcontroller to a defined state. The Reset configuration

is shown in Fig.5.

Fig.4 External components for RESET pin.

andbook, halfpage

VSS

≤ 100 kΩ

RESET

MCD174

7.1

Power-on-reset

The Power-on-reset circuit monitors the voltage level of

VDD. If VDD remains below the internal reference voltage

level Vref (typically 1.3 V), the oscillator is inhibited.

When VDD rises above Vref, the oscillator is released and

the internal reset is active for a period of td (typically

µs).

Considering the VDD rise time, the following measures for

a correct Power-on-reset can be taken:

• If the VDD rises above the minimum operation voltage

before time period td is exceeded, no external

components are necessary (see Fig.6).

• If V

DD has a slow rise time, such that after the time

period (tVref +td) has elapsed the supply voltage is still

below the minimum operation voltage (Vmin),

external components are required (see Figs 4 and 7).

To guarantee a correct reset operation, ensure that the

time constant RC

≥ 8 × tVDD.

A definite Power-on-reset can be realized by applying an

(external) RESET signal during power-on.

Fig.5 Reset configuration.

handbook, full pagewidth

MLA651

RESET

POWER-ON-RESET

oscillator

inhibit

ref

internal

reset

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