HT56R67 datasheet(82/104 Pages) HOLTEK

82 / 104 page

HT56R67/HT56R668/HT56C668/HT56R678/HT56C678/HT56R688

Rev. 1.20

March 4, 2010

Low Voltage Detector

- LVD

The Low Voltage Detect internal function provides a

means for the user to monitor when the power supply

voltage falls below a certain fixed level as specified in

the DC characteristics.

LVD Operation

The LVD function must be first enabled via a configura-

tion option after which bits 3 and 5 of the RTCC register

are used to control the overall function of the LVD. Bit 3

is the enable/disable control bit and is known as LVDC,

when set low the overall function of the LVD will be dis-

abled. Bit 5 is the LVD detector output bit and is known

as LVDO. Under normal operation, and when the power

supply voltage is above the specified VLVD value in the

DC characteristic section, the LVDO bit will remain at a

zero value. If the power supply voltage should fall below

this VLVD value then the LVDO bit will change to a high

value indicating a low voltage condition. Note that the

LVDO bit is a read-only bit. By polling the LVDO bit in the

RTCC register, the application program can therefore

determine the presence of a low voltage condition.

After power-on, or after a reset, the LVD will be switched

off by clearing the LVDC bit in the RTCC register to zero.

Note that if the LVD is enabled there will be some power

consumption associated with its internal circuitry, how-

ever, by clearing the LVDC bit to zero the power can be

minimised. It is important not to confuse the LVD with

the LVR function. In the LVR function an automatic reset

will be generated by the microcontroller, whereas in the

LVD function only the LVDO bit will be affected with no

influence on other microcontroller functions.

There are a range of voltage values, selected using a

configuration option, which can be chosen to activate

the LVD.

Watchdog Timer

The Watchdog Timer is provided to prevent program

malfunctions or sequences from jumping to unknown lo-

cations, due to certain uncontrollable external events

such as electrical noise. It operates by providing a de-

vice reset when the Watchdog Timer counter overflows.

Watchdog Timer Operation

The Watchdog Timer clock source is provided by the in-

ternal clock, fS, which is in turn supplied by one of two

sources selected by configuration option: fSUB or fSYS/4.

Note that if the Watchdog Timer configuration option

has been disabled, then any instruction relating to its op-

eration will result in no operation.

Most of the Watchdog Timer options, such as en-

able/disable, Watchdog Timer clock source and clear in-

struction type are selected using configuration options.

In addition to a configuration option to enable the Watch-

dog Timer, there are four bits, WDTEN3~ WDTEN0, in

the MISC register to offer an additional enable control of

the Watchdog Timer. These bits must be set to a specific

value of 1010 to disable the Watchdog Timer. Any other

values for these bits will keep the Watchdog Timer en-

abled. After power on these bits will have the disabled

value of 1010.

W D T S o u r c e

C o n f i g u r a t i o n

O p t i o n

C o n t r o l

L o g i c

C L R W D T 1 F l a g

C L R W D T 2 F l a g

1 o r 2 I n s t r u c t i o n s

f S Y S / 4

W D T O s c i l l a t o r

8 - b i t D i v i d e r

f S

C L R

W D T T i m e - o u t

( 2 1 3 / f S , 2 1 4 / f S , 2 1 5 / f S o r 2 1 6 / f S )

¸ 2

7 - b i t P r e s c a l e r

f S / 2 8

f S / 2 1 2 , f S / 2 1 3 , f S / 2 1 4 o r f S / 2 1 5

C o n f i g O p t i o n

R T C O s c i l l a t o r

Watchdog Timer

M I S C R e g i s t e r

b 7

W D T E N 0

b 0

W D T E N 1

P A 0 ~ P A 3 O p e n D r a i n C o n t r o l

- d e s c r i b e d e l s e w h e r e

W a t c h d o g T i m e r E n a b l e C o n t r o l

O D E 0

W D T E N 3

W D T E N 2

W D T E N 3

O D E 1

O D E 2

O D E 3

W D T E N 2

W D T E N 1

W D T E N 0

d i s a b l e

e n a b l e

a l l o t h e r v a l u e s

Watchdog Timer Software Control

- MISC

HT56R67 Datasheet(PDF) 82 Page - Holtek Semiconductor Inc

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