HT46R321 datasheet(9/45 Pages) HOLTEK

9 / 45 page

HT46R321

Rev. 1.00

August 3, 2007

pointer is decremented, using a RET or RETI instruc-

tion, the interrupt will be serviced. This feature prevents

a stack overflow allowing the programmer to use the

structure more easily. In a similar case, if the stack is full

and a

²CALL² is subsequently executed, stack overflow

occurs and the first entry will be lost. Only the most re-

cent 6 return addresses are stored.

Data Memory

- RAM

The data memory is divided into two functional groups:

special function registers and general purpose data

memory. The general purpose memory has a structure

of 88

´8 bits. Most locations are read/write, but some

are read only.

The remaining space between the end of the Special

Purpose Data Memory and the beginning of the General

Purpose Data Memory is reserved for future expanded

usage, reading these locations will obtain a result of

²00H². The general purpose data memory, addressed

from 28H to 7FH, is used for user data and control infor-

mation under instruction commands. All of the data

memory areas can handle arithmetic, logic, increment,

decrement and rotate operations directly. Except for

some dedicated bits, each bit in the data memory can

be set and reset by the

²SET [m].i² and ²CLR [m].i² in-

structions. They are also indirectly accessible through

memory pointer register, MP.

Indirect Addressing Register

Location 00H is an indirect addressing register that is

not physically implemented. Any read/write operation on

[00H] accesses data memory pointed to by the MP

the result 00H. Writing indirectly results in no operation.

The memory pointer register, MP, is a 7-bit register. The bit 7

of MP is undefined and read as

²1².

Accumulator

The accumulator is closely related to ALU operations

and can carry out immediate data operations. Any data

movement between two data memory locations must

pass through the accumulator.

Arithmetic and Logic Unit

- ALU

This circuit performs 8-bit arithmetic and logic opera-

tions. The ALU provides the following functions:

· Arithmetic operations - ADD, ADC, SUB, SBC, DAA

· Logic operations - AND, OR, XOR, CPL

· Rotation - RL, RR, RLC, RRC

· Increment and Decrement - INC, DEC

· Branch decision - SZ, SNZ, SIZ, SDZ ....

The ALU not only saves the results of a data operation but

also changes the status register.

S p e c i a l P u r p o s e

D a t a M e m o r y

0 0 H

0 1 H

0 2 H

0 3 H

0 4 H

0 5 H

0 6 H

0 7 H

0 8 H

0 9 H

0 A H

0 B H

0 C H

0 D H

0 E H

0 F H

1 0 H

1 1 H

1 2 H

1 3 H

1 4 H

1 5 H

1 6 H

1 7 H

1 8 H

1 9 H

1 A H

1 B H

1 C H

1 D H

1 E H

1 F H

I n d i r e c t A d d r e s s i n g R e g i s t e r

M P

A C C

P C L

T B L P

T B L H

S T A T U S

I N T C

T M R

T M R C

P A

P A C

P B

P B C

P D

P D C

P W M 0

P W M 1

O P A C

A D R L

A D R H

A D C R

A C S R

: U n u s e d

R e a d a s " 0 0 "

2 0 H

2 1 H

2 2 H

2 3 H

2 7 H

2 4 H

7 F H

2 8 H

G e n e r a l P u r p o s e

D a t a M e m o r y

( 8 8 B y t e s )

RAM Mapping

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