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HTG1390

4-bit Microcontroller

Holtek Semiconductor 

Preliminary

HTG1390

Timer

The HTG1390 contains a programmable 8-bit count-

up counter which can be used as a clock to generate

an accurate time base.

The Timer may be set and read with software

instructions and stopped by a hardware reset or

a TIMER OFF instruction. To restart the timer

load the counter with the value XXH and then

issue a TIMER ON instruction. Note that XX is

the desired start count immediate value of the

8 bits. Once the Timer/Counter is started it

increments to a maximum count of FFH and

then overflows to zero (00H). It then continues

to count until stopped by a TIMER OFF instruc-

tion or a reset.

The increment from the maximum count of

FFH to a zero (00H) triggers a timer flag TF and

an internal interrupt request. The interrupt

may be enabled or disabled by executing the EI

and DI instruction. If the interrupt is enabled

the timer overflow will cause a subroutine call

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

testable 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.

Note that n cannot have the value of 6, which is

reserved for internal use.

Interrupt

The HTG1390 provides both internal and exter-

nal interrupt modes. The DI and EI instruc-

tions are used to disable and enable the

interrupts. During Halt mode, if the PP or PS

input pin is triggered on a high to low transition

in the enable interrupt mode and the program

is not within a CALL subroutine, the external

interrupt is actived. This causes a subroutine

call to location 8 and resets 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 internal inter-

rupt is activated. This causes a subroutine call

to location 4 and resets the timer flag.

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 behaviour may

occur. If within a CALL subroutine internal

interrupt occur, the internal interrupt will be

serviced after leaving the CALL subroutine.

The interrupts are disabled by a hardware reset

or a DI instruction. They remain disabled until

the EI instruction is executed.

Each input port pin can be programmed by

mask option to have an external interrupt func-

tion in the HALT mode.

Initial reset

The HTG1390 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, 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 for at least 5ms. Normal cir-

cuit operation will not commence until the RES

pin returns high.

The reset performs the following functions:

PC

000H

TIMER

Stop

Time flag

Reset (Low)

SOUND

Sound off and one sing

mode

Output Port A

high (or floating state)

Interrupt

Disabled

BZ and BZ output Low level

9

17th Nov ’98

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