HT45R37V datasheet(63/90 Pages) HOLTEK

63 / 90 page

HT45R37V

Rev. 1.00

October 20, 2009

· 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. The RES pin is shared with an I/O

pin so its function must be first selected using a config-

uration option.

· Low Voltage Reset - LVR

The microcontroller contains a low voltage reset circuit

in order to monitor the supply voltage of the device,

which 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 bat-

tery, the LVR will automatically reset the device inter-

nally. The LVR includes the following specifications: For

a valid LVR signal, a low voltage, i.e., a voltage in the

range between 0.9V~VLVR must exist for greater than the

value tLVR specified in the A.C. characteristics. If the low

voltage state does not exceed 1ms, the LVR will ignore it

and will not perform a reset function. One of a range of

specified voltage values for VLVR can be selected using

configuration options. The VLVR value will be selected as

a pair in conjunction with a Low Voltage Detect value.

· 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 Counter Timer Counter will be turned off

Prescaler

The Timer Counter Prescaler

will be cleared

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

C h i p 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

R E S

S S T T i m e - o u t

C h i p 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

C h i p R e s e t

t R S T D

Low Voltage Reset Timing Chart

HT45R37V Datasheet(PDF) 63 Page - Holtek Semiconductor Inc

HT45R37V Datasheet(HTML) 63 Page - Holtek Semiconductor Inc

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