HT46R652 datasheet(15/47 Pages) HOLTEK

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HT46R652

Rev. 1.00

December 19, 2006

Real Time Clock

- RTC

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

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

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

8 to

fS/2

15, the value being setup using software. Writing

data to the RT2, RT1 and RT0 bits in the RTCC register,

provides various time-out periods. If an RTC time-out

occurs, the related interrupt request flag, RTF; bit 6 of

INTC1, is set. But if the interrupt is enabled, and the

stack is not full, a subroutine call to location 18H occurs.

RT2

RT1

RT0

RTC Clock Divided Factor

000

001

010

10*

011

11*

100

101

110

111

Note: * not recommended to be used

Power Down Operation

The Power Down mode is entered by the execution of a

²HALT² instruction and results in the following.

· The system will cease to run but the WDT oscillator

will keep running if the WDT oscillator or the real time

clock is selected.

· The contents of the Memory and registers remain un-

changed.

· The WDT will be cleared and starts recounting, if the

WDT clock source is sourced from the WDT oscillator

or the real time clock oscillator.

· All I/O ports maintain their original status.

· The PDF flag is set but the TO flag is cleared.

· The LCD driver will maintain its function if the WDT

OSC or RTC OSC is selected.

The system will wake up from the Power Down mode via

an external reset, an interrupt, an external falling edge

signal on port A or a WDT overflow. An external reset will

generate a device initialisation, while a WDT overflow

performs a

²warm reset². After examining the TO and

PDF flags, the reason for the device reset can be deter-

mined. The PDF flag is cleared by a system power-up or

by executing the

²CLR WDT² instruction, and is set by

executing the

²HALT² instruction. The TO flag is set if a

WDT time-out occurs, and causes a wake-up that only

resets the Program Counter and the Stack Pointer, but

leaves the others in their original state.

The port A wake-up and interrupt methods can be con-

sidered as a continuation of normal execution. Each bit

in port A can be independently selected to wake up the

device by a configuration option. If awakened by an I/O

port stimulus, the program resumes execution at the

next instruction following the

²HALT² instruction. Awak-

ening from an interrupt, two sequence may occur. If the

related interrupt is disabled or the interrupt is enabled

but the stack is full, the program resumes execution at

the next instruction. But if the interrupt is enabled, and

the stack is not full, a regular interrupt response takes

place.

When an interrupt request flag is set before entering the

Power Down mode, the system cannot be awakened us-

ing that interrupt.

If a wake-up events occur, it takes 1024 tSYS (system

clock periods) to resume normal operation. In other

words, a dummy period is inserted after the wake-up. If

the wake-up results from an interrupt acknowledgment,

the actual interrupt subroutine execution is delayed by

more than one cycle. However, if a wake-up results in

the next instruction execution, the execution will be per-

formed immediately after the dummy period is finished.

To minimise power consumption, all the I/O pins should

be carefully managed before entering the Power Down

mode.

Reset

There are three ways in which a reset may occur.

· RES pin is pulled low during normal operation

· RES pin is pulled low when in the Power Down mode

· A WDT time-out during normal operation

A WDT time-out when the device is in the Power Down

mode differs from other device reset conditions, as it will

perform a

²warm reset² that resets only the program

counter and the SP but leaves the other circuits in their

original state. Some registers remain unaffected during

other reset conditions. Most registers are reset to their

initial condition once the reset conditions are met. By ex-

amining the PDF and TO flags, the program can distin-

guish between the different types of device resets.

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

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

Real Time Clock

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