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HTG12N0

4-Bit Microcontroller

Holtek Semiconductor 

HTG12N0

may be enabled or disabled by executing the EI

and DI instructions. If the interrupt is enabled

the timer overflow will cause a subroutine call

to location 4. The state of the timer flag can also

be tested with the conditional jump instruction

JTMR. The timer flag is cleared after the inter-

rupt or the JTMR instruction is executed.

If an internal source is used, the frequency is

determined by the system clock and the pa-

rameter n as defined in the equation. The fre-

quency of the internal frequency source can be

selected by mask option.

Frequency of TIMER clock =

system clock

2n

where n=0,1,2 ...13 selectable by mask option.

RTC

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

mented on the HTG12N0. The RTC function is used

to generate an accurate time period. The clock source

of RTC circuit comes from the 32768Hz crystal oscil-

lator. The block diagram is shown as follows.

The RTC output 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 HTG12N0 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 inter-

rupt mode and the program is not within a

CALL subroutine, this causes a subroutine call

to location 8 and reset the interrupt latch.

Likewise when the timer flag is set in the en-

able interrupt mode and the program is not

within a CALL subroutine, the TIMER inter-

rupt is activated. 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 one will be serviced first.

When running under a CALL subroutine or DI

the interrupt acknowledge is on hold until the

RET or EI instruction a 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 interrupt arrive at

the same time.

The interrupt are disabled by a hardware reset

or a DI instruction. They remain disabled until

the EI instruction is executed.

Initial reset

The HTG12N0 provides an RES pin for system

initialization. This pin is equipped with an in-

ternal pull high resistor and in combination

with an external 0.1µ~1µF capacitor, it provides

an internal reset pulse of sufficient length to

guarantee a reset to all internal circuits. If the

reset pulse is generated externally, the RES pin

must be held low at least 5ms.

When RES is active, the internal block will be

initialized as shown below:

PC

000H

TIMER

Stop

Timer flag,

Carry 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

11

18th Mar ’99

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