HT47C20L datasheet(17/55 Pages) HOLTEK

17 / 55 page

HT47C20L

January 18, 2000

Time base

The time base offers a periodic time-out period to

generate a regular internal interrupt. Its time-out

period ranges from fs/212 to fs/215 selected by mask

option. If time base time-out occurs, the related

interrupt request flag (TBF; bit 5 of INTC0) is set.

But if the interrupt is enabled, and the stack is

not full, a subroutine call to location 08H occurs.

When the HALT instruction is executed, the time

base still works and can wake up from halt mode.

If the TBF is set ²1² before entering the halt

mode, the wake up function will be disabled.

Real time clock - RTC

The real time clock is operated in the same

manner as the time base that is used to supply

a regular internal interrupt. Its time-out period

ranges from fs/28 to fs/215 by software program-

ming. Writing data to RT2, RT1 and RT0 (bits 2,

1, 0 of RTCC;09H) yields various time-out

periods. If a real time clock time-out occurs, the

related interrupt request flag (RTF; bit 6 of

INTC0) is set. But if the interrupt is enabled,

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

cation 0CH occurs. The real time clock time-out

signal can also be applied as a clock source of

timer/event counter A, so as to get a longer

time-out period.

RT2

RT1

RT0 RTC Clock Divided

Factor

210

211

212

213

214

215

Power down operation - HALT

The halt mode is initialized by the HALT in-

struction and results in the following.

· The 32768Hz crystal oscillator will still work

but the system clock and T1 will turn off.

· The contents of the on-chip RAM and regis-

ters remain unchanged.

· The WDT will be cleared and recount again.

· All I/O ports maintain their original status.

· The PD flag is set and the TO flag is cleared.

· LCD driver is still running (by mask option).

· The time base and real time clock will still

work.

D i v i der

Ma s k O pt i o n

Pr e s c a l e r

LC D D r i v er

T i m e B as e I n t e r r upt

f s /2

~ f s /2

Bu z z e r

f s /2 ~ f s /2

f s /8

f s /2

f s

Time base

D i v i der

8 t o 1

Mu x .

P r e sca l e r

RT 2

RT 1

RT 0

R eal T i m e C l oc k I n t e r r upt

f s /2 ~ f s /2

f s /2

f s

Real time clock

HT47C20L Datasheet(PDF) 17 Page - Holtek Semiconductor Inc

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