HT68F13 datasheet(43/161 Pages) HOLTEK

43 / 161 page

RES PinReset

As the reset pin is shared with PB.3, the reset function must be selected using a configuration option.

Although the microcontroller has an internal RC reset function, if the VDD power supply rise time is

not fast enough or does not stabilise quickly at power-on, the internal reset function may be

incapable of providing proper reset operation. For this reason it is recommended that an external RC

network is connected to the RES pin, whose additional time delay will ensure that the RES pin

remains low for an extended period to allow the power supply to stabilise. During this time delay,

normal operation of the microcontroller will be inhibited. After the RES line reaches a certain

voltage value, the reset delay time tRSTD is invoked to provide an extra delay time after which the

microcontroller will begin normal operation. The abbreviation SST in the figures stands for System

Start-up Timer. For most applications a resistor connected between VDD and the RES pin and a

capacitor connected between VSS and the RES pin will provide a suitable external reset circuit. Any

wiring connected to the RES pin should be kept as short as possible to minimise any stray noise

interference. For applications that operate within an environment where more noise is present the

Enhanced Reset Circuit shown is recommended.

More information regarding external reset circuits is located in Application Note HA0075E on the

Holtek website.

Pulling the RES Pin low using external hardware will also execute a device reset. In this case, as in the

case of other resets, the Program Counter will reset to zero and program execution initiated from this

point.

HT68F13/HT68F14/HT68F15

EnhancedI/OFlashType MCU

Rev.1.10

February9,2011

R E S

I n t e r n a l R e s e t

0 . 9 V D D

0 . 4 V D D

t R S T D + t S S T

Note: tRSTD ispower-ondelay,typicaltime=100ms

RES ResetTimingChart

P B 3 / R E S

0 . 1 ~ 1 m F

1 0 k W ~

1 0 0 k W

V D D

V S S

0 . 0 1 m F * *

V D D

1 N 4 1 4 8 *

3 0 0 W *

Note:

²*² Itisrecommendedthatthiscomponentisaddedforadded ESD protection

²**² It is recommended that this component is added in environments where power line noise

issignificant

External RES Circuit

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