HT49C30L datasheet(14/43 Pages) HOLTEK

14 / 43 page

HT49R30A-1/HT49C30-1/HT49C30L

Rev. 1.10

September 25, 2002

external reset (a low level to RES), software instruction,

and a

²HALT² instruction. There are two types of soft-

ware instructions;

²CLR WDT² and the other set -²CLR

WDT1

² and ²CLR WDT2². Of these two types of instruc-

tion, only one type of instruction can be active at a time

depending on the options

-²CLR WDT² times selection

option . If the

²CLR WDT² is selected (i.e., CLR WDT

times equal one), any execution of the

²CLR WDT² in-

struction clears the WDT. In the case that

²CLR WDT1²

and

²CLR WDT2² are chosen (i.e., CLR WDT times

equal two), these two instructions have to be executed

to clear the WDT; otherwise, the WDT may reset the

chip due to time-out.

Multi-function timer

The device provides a multi-function timer for the WDT,

time base and RTC but with different time-out periods.

The multi-function timer consists of a 8-stage divider

and an 7-bit prescaler, with the clock source coming

from the WDT OSC or RTC OSC or the instruction clock

(i.e.., system clock divided by 4). The multi-function

timer also provides a selectable frequency signal

(ranges from fS/2

2 to f

S/2

8) for LCD driver circuits, and a

selectable frequency signal (ranges from fS/2

2 to f

S/2

for the buzzer output by options. It is recommended to

select a near 4kHz signal to LCD driver circuits for

proper display.

Time base

The time base offers a periodic time-out period to gener-

ate a regular internal interrupt. Its time-out period

ranges from /2

12 to f

S/2

15 selected by options. If time

base time-out occurs, the related interrupt request flag

(TBF; bit 4 of INTC1) is set. But if the interrupt is en-

abled, and the stack is not full, a subroutine call to loca-

tion 10H occurs.

Real time clock

- RTC

The real time clock (RTC) is operated in the same man-

ner as the time base that is used to supply a regular in-

ternal interrupt. Its time-out period ranges from fS/2

8 to

fS/2

15 by software programming . Writing data to RT2,

RT1 and RT0 (bit2, 1, 0 of RTCC;09H) yields various

time-out periods. If the RTC time-out occurs, the related

interrupt request flag (RTF; bit 5 of INTC1) is set. But if

the interrupt is enabled, and the stack is not full, a sub-

routine call to location 14H occurs. The real time clock

time-out signal also can be applied to be a clock source

of timer/event counter for getting a longer time-out pe-

riod.

f s

T i m e B a s e I n t e r r u p t

f S / 2 1 2 ~ f S / 2 1 5

B u z z e r ( f S / 2 2 ~ f S / 2 9 )

L C D D r i v e r ( f S / 2 2 ~ f S / 2 8 )

D i v i d e r

P r e s c a l e r

O p t i o n

Time base

D i v i d e r

f S

8 t o 1

M u x .

P r e s c a l e r

R T 2

R T 1

R T 0

R T C I n t e r r u p t

f S / 2 8 ~ f S / 2 1 5

Real time clock

S y s t e m C l o c k / 4

D i v i d e r

W D T C l e a r

O p t i o n

S e l e c t

W D T

O S C 1 2 k H z

R T C

O S C 3 2 7 6 8 H z

C K T

f S

T i m e - o u t R e s e t f S / 2 1 5 ~ f S / 2 1 6

D i v i d e r

Watchdog Timer

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