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HTG12G0

Microcontroller

Holtek Semiconductor 

HTG12G0

RTC

There is a real time clock (RTC) function imple-

mented on the HTG12G0. The RTC function is

used to generate an accurate time period. The

clock source of the RTC circuit comes from the

32768Hz crystal oscillator. The block diagram is

shown as follows:

The output of the RTC can be selected by mask

option.

Frequency of the RTC output =

256

2n

n=0~7

The RTC output is used to generate an inter-

rupt signal.

Interrupt

The HTG12G0 provides both TIMER and RTC

interrupt modes. The DI and EI instructions are

used to disable and enable the interrupts. When

the RTC is activated during enable interrupt

mode and the program is not within a CALL

subroutine, this causes a subroutine call to loca-

tion 8 and reset the interrupt latch.

Likewise when the timer flag is set in the enable

interrupt mode and the program is not within a

CALL subroutine, the TIMER interrupt is acti-

vated. This cause a subroutine call to location 4

and resets the timer flag. If both TIMER and

RTC interrupts arrive at the same time, the

RTC will be serviced first.

When running under a CALL subroutine or DI

the interrupt acknowledge is on hold until the

RET or EI instruction is invoked. The CALL

instruction should not be used within an inter-

rupt routine as unpredictable behaviors may

occur. If within a CALL subroutine both TIMER

and RTC interrupt occur, no matter what order

they arrive in, the RTC interrupt will be serv-

iced first after leaving the CALL subroutine.

This also applies if the two interrupts arrive at

the same time.

The interrupts are disabled by a hardware reset

or a DI instruction. They remain disabled until

the EI instruction is executed.

Initial reset

The HTG12G0 provides a RES pin for system

initialization. Since the RES pin has internal

pull high resistor, only an external 0.1µ~1µ ca-

pacitor is needed. If the reset pulse is gene-

rated externally, it must be held low for at least

5 ms.

When RES is active, the internal block will be

initialized as shown below:

PA3 and PC 1000H

TIMER

Stop

Timer flag

Reset (low)

SOUND

Sound off and one sing mode

Output port A High (or floating state)

LCD output Disabled

BZ and BZ

output

High level

HALT

This is a special feature of HTG12G0. It will

stop the chip’s normal operation and reduces

power consumption. When the instruction

“HALT” is executed, then

• System oscillator will be stopped

• The contents of the on-chip RAM and

registers remain unchanged

• RTC oscillator still keeps running

The system can escape HALT mode by ways of

initial reset or RTC interrupt or wake-up from

the following entry of program counter value.

• Initial reset: 1000H

Wake-up: next address of the HALT instruc-

tion

When the halt status is terminated by the

RTC interrupt, the following procedure takes

place:

* Case1: If the system is in an interrupt-dis-

able state before entering the halt state:

11

14th May ’99

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