HT95R45 datasheet(43/76 Pages) HOLTEK

43 / 76 page

HT95R45

Rev. 1.00

March 12, 2010

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.

· 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.

Reset Initial Conditions

The different types of reset described affect the reset

flags in different ways. These flags, known as PDF and

TO are located in the status register and are controlled

by various microcontroller operations, such as the

Power Down function or Watchdog Timer. The reset

flags are shown in the table:

TO PDF

RESET Conditions

RES reset during power-on

RES or LVR reset during normal operation

WDT time-out reset during normal operation

WDT time-out reset during Power Down

Note:

²u² stands for unchanged

The following table indicates the way in which the vari-

ous components of the microcontroller are affected after

a power-on reset occurs.

Item

Condition After RESET

Program Counter

Reset to zero

Interrupts

All interrupts will be disabled

WDT

Clear after reset, WDT begins

counting

Timer/Event

Counters

The Timer Counters will be

turned off

Input/Output Ports

I/O ports will be setup as inputs

Stack Pointer

Stack Pointer will point to the top

of the stack

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

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

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

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

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