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HTG12G0

Microcontroller

Holtek Semiconductor 

HTG12G0

Working registers – R0, R1, R2, R3, R4

These five registers are usually used to store the

frequently accessed data. The working register

can be incremented (+1) or decremented (–1).

The JNZ Rn,address (n=0,1,4) instruction

makes very efficient use of the working register

as program loop counter. The register pairs of

R1, R0 and R3, R2 can also be used as the data

memory pointer, when the data memory trans-

fer instruction is executed.

Data memory – RAM

The data memory is a static RAM organized

with 256 × 4 bits and is used to store temporary

data and display data. All of the data memory

locations are indirectly addressable through the

register pair “R1, R0” or “R3, R2”.

There are two areas in the data memory, tempo-

rary data area and display data area. Access to

temporary data memory is made through

00H~9BH address, and access to display data

memory is made in 9CH~FFH address.

When data is written in the display area, the

LCD driver automatically reads it and gene-

rates an LCD driving signal.

Data memory

Accumulator – ACC

The register ACC plays the most important role

in data manipulation and data transfer. It is not

only one of the sources of input to the ALU but

also the destination of the result due to ALU.

Data transfer can be performed between ACC

and other registers, data memory or I/O ports.

Arithmetic and logic unit – ALU

This circuit performs arithmetic and logic op-

eration. The ALU provides the following func-

tions:

• Arithmetic operation

(ADD, ADC, SUB, SBC, DAA)

• Logic operation (AND, OR, XOR)

• Rotation (RL, RR, RLC, RRC)

• Increment and Decrement (INC, DEC)

• Branch decision (JZ, JNZ, JC, JNC...)

The ALU not only outputs the results of data

operation but also sets the status of carry flag

(C) in some instructions.

Timer

This is a programmable 8–bit count-up counter,

internal frequency sources used to aid the user

in counting and generating accurate time base.

The Timer can be pre-set and read with soft-

ware instructions. “TIMER XXH”, “MOV

TMRL, A” and “MOV TMRH, A” preload TIMER

value. “MOV A, TMRL” and “MOV A, TMRH”

read the contents of TIMER to ACC.

The Timer is stopped by a hardware reset or

“TIMER OFF” instruction and started by a

TIMER ON instruction.

Once the Timer is started, it will increment to

its maximum count (FFH) and overflows to zero

(00H). It will not stop until there is a “TIMER

OFF” instruction or reset. When an overflow

occurs, it will set the Timer Flag (TF) simulta-

neously. If interrupt is enabled, the Timer cir-

cuit supports TF for internal interrupt. The

state of the TF can be tested with the condi-

tional instruction JTMR.

The Timer flag is cleared after the interrupt or

JTMR instruction is executed.

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......13 except 6, by mask option

(the sixth stage is reserved for internal use).

10

14th May ’99

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