HTG12B0 データシートの表示（PDF） - Holtek Semiconductor

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HTG12B0

4-Bit Microcontroller

Holtek Semiconductor 

HTG12B0

The locations between the temporary and

display data areas are undefined and cannot be

used.

Accumulator - ACC

The accumulator is the most important data

register in the processor. It is one of the sources

of input to the ALU and the destination of the

results of the operations performed in the ALU.

Data to and from the I/O ports and memory also

passes through the accumulator.

Arithmetic and logic unit - ALU

This circuit performs the following arithmetic

and logic operations ...

· Add with or without carry

· Subtract with or without carry

· AND, OR, Exclusive-OR

· Rotate right, left through carry

· BCD decimal adjust for addition

· Increment, decrement

· Data transfers

· Branch decisions

The ALU not only outputs the results of data

operations, but also sets the status of the carry

flag (CF) in some instructions.

Timer/counter

The HTG12B0 contains a programmable 8-bit

count-up counter which can be used to count external

events or used as a clock to generate an accurate

time base.

If the 8-bit timer clock is supplied by an exter-

nal source from pin TMCLK, synchronization

problems may occur when reading the data

from the timer. It is therefore recommended

that the timer is stopped before retrieving the

data. The 8-bit counter will increment on the

rising edge of the clock whether it is internally

or externally generated.

The Timer/Counter may be set and read with

software instructions and stopped by a hard-

ware reset or a TIMER OFF instruction. To re-

start the timer, load the counter with the value

XXH and then issue a TIMER ON instruction.

Note that XX is the desired start count immedi-

ate 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 instruction 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 inter-

rupt may be enabled or disabled by executing

the EI and DI instructions. If the interrupt is

enabled, the timer overflow will cause a subrou-

tine call to location 4. The state of the timer flag

can also be tested with the conditional jump in-

struction JTMR. The timer flag is cleared after

the interrupt or the JTMR instruction is exe-

cuted.

If an internal source is used, the frequency is

determined by the system clock and the param-

eter n as defined in the equation. The frequency

of the internal frequency source can be selected

by mask option.

Frequency of TIMER clock =

system clock

2n

where n=0, 1, 2... 3 selectable by mask option.

RTC

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

mented on the HTG12B0. The RTC function is

used to generate an accurate time period. The

RTC circuit clock source comes from the 32768Hz

crystal oscillator. The block diagram is shown as

follows.

X 'ta l 3 2 7 6 8 H z

1

128

1

2n , n = 0 ~ 7

M a s k O p tio n

In te rru p t

The output of RTC can be selected by mask op-

tion.

Frequency of RTC output =

256

2n

,

n=0~7

The RTC output is used to generate an inter-

rupt signal.

10

September 8, 1999

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