HT82B40R datasheet(24/57 Pages) HOLTEK

24 / 57 page

HT82B40R/HT82B40A

Rev. 1.10

September 4, 2009

For most applications a resistor connected between

VDD and the RES pin and a capacitor connected be-

tween VSS and the RES pin will provide a suitable ex-

ternal 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 Cir-

cuit shown is recommended.

More information regarding external reset circuits is

located in Application Note HA0075E on the Holtek

website.

· RES Pin Reset

This type of reset occurs when the microcontroller is

already running and the RES pin is forcefully pulled

low by external hardware such as an external switch.

In this case as in the case of other reset, the Program

Counter will reset to zero and program execution initi-

ated from this point. Note that as the external reset pin

is also pin-shared with PA7, if it is to be used as a reset

pin, the correct reset configuration option must be se-

lected.

· Low Voltage Reset

- LVR

The microcontroller contains a low voltage reset cir-

cuit in order to monitor the supply voltage of the de-

vice. The LVR function is selected via a configuration

option. If the supply voltage of the device drops to

within a range of 0.9V~VLVR such as might occur when

changing the battery, the LVR will automatically reset

the device internally. For a valid LVR signal, a low sup-

ply voltage, i.e., a voltage in the range between

0.9V~VLVR must exist for a time greater than that spec-

ified by tLVR in the A.C. characteristics. If the low sup-

ply voltage state does not exceed this value, the LVR

will ignore the low supply voltage and will not perform

a reset function. The actual VLVR value can be se-

lected via configuration options.

· Watchdog Time-out Reset during Normal Operation

The Watchdog time-out Reset during normal opera-

tion is the same as a hardware RES pin reset except

that the Watchdog time-out flag TO will be set to

²1².

· Watchdog Time-out Reset during Power Down

The Watchdog time-out Reset during Power Down is

a little different from other kinds of reset. Most of the

conditions remain unchanged except that the Pro-

gram Counter and the Stack Pointer will be cleared to

²0² and the TO flag will be set to ²1². Refer to the A.C.

Characteristics for tSST details.

R E S

0 . 1 m F

1 0 0 k W

V D D

V S S

0 . 0 1 m F

1 0 k W

Enhanced Reset Circuit

R E S

V D D

S S T T i m e - o u t

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

0 . 9 V D D

t R S T D

Power-On Reset Timing Chart

R E S

V D D

V S S

0 . 1 m F

1 0 0 k W

Basic Reset Circuit

R E S

S S T T i m e - o u t

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

RES Reset Timing Chart

L V R

S S T T i m e - o u t

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

t R S T D

Low Voltage Reset Timing Chart

W D T T i m e - o u t

S S T T i m e - o u t

t S S T

WDT Time-out Reset during Power Down

Timing Chart

W D T T i m e - o u t

S S T T i m e - o u t

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

t R S T D

WDT Time-out Reset during Normal Operation

Timing Chart

HT82B40R Datasheet(PDF) 24 Page - Holtek Semiconductor Inc

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