HTG12N0 データシートの表示（PDF） - Holtek Semiconductor

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HTG12N0

4-Bit Microcontroller

Holtek Semiconductor 

HTG12N0

Data memory – RAM

The static data memory (RAM) is arranged in

256×4 bit format and is used to store data. All of

the data memory locations are indirectly ad-

dressable through the register pair R1,R0 or

R3,R2; for example MOV A,[R3R2] or MOV

[R3R2],A.

There are two banks for data memory in

HTG12N0, each bank shown in the figure can

be switched by the assignment of PC0. Each

bank maps to different area of the data memory.

There are two areas in the data memory, the

temporary data area and the display data area.

Access to the temporary data area is from 00H

to 7FH of bank 0 and 00H to 7FH of bank 1,

Locations 80H to FFH (don’t care the bank

pointer) represent the display data area.

When data is written into the display data area

it is automatically read by the LCD driver

which then generates the corresponding LCD

driving signals.

The relationship between the data pointer RAM

locations are shown in the table.

Data memory

Data memory

Display data area (80H~FFH) don’t care about

the PC0.

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 logical 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 HTG12N0 contains a programmable 8-bit

count-up counter which can be used to count

external events or 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 suggested 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

restart the timer, load the counter with the

value XXH and then issue a TIMER ON in-

struction. 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 instruction or a reset.

The increment from the maximum count of

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

an internal interrupt request. The interrupt

10

18th Mar ’99

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