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HT48RA0-1

Remote Type 8-Bit MCU

Holtek Semiconductor 

HT48RA0-1/HT48CA0-1

0 0 H In d ir e c t A d d r e s s in g R e g is te r

01H

MP

02H

03H

04H

05H

ACC

06H

PCL

07H

TB LP

08H

TB LH

09H

0A H

STATU S

0B H

0C H

0D H

0E H

0FH

10H

11H

12H

PA

13H

14H

PB

15H

16H

PC

17H

1FH

20H

G e n e ra l P u rp o s e

D a ta M e m o ry

(3 2 B y te s )

3FH

S p e c ia l P u r p o s e

D a ta M e m o ry

:U nused

R e a d a s "0 0 "

RAM Mapping

counter lower-order byte register (PCL;06H), the table

pointer (TBLP;07H), the table higher-order byte register

(TBLH;08H), the status register (STATUS;0AH) and the

I/O registers (PA;12H, PB;14H, PC;16H). The remaining

space before the 20H is reserved for future expanded

usage and reading these locations will return the result

00H. The general purpose data memory, addressed

from 20H to 3FH, is used for data and control informa-

tion under instruction command.

All data memory areas can handle arithmetic, logic, in-

crement, decrement and rotate operations directly. Ex-

cept for some dedicated bits, each bit in the data

memory can be set and reset by the SET [m].i and CLR

[m].i instructions, respectively. They are also indirectly

accessible through memory pointer register (MP;01H).

Indirect Addressing Register

Location 00H is an indirect addressing register that is

not physically implemented. Any read/write operation of

[00H] accesses data memory pointed to by MP (01H).

Reading location 00H itself indirectly will return the re-

sult 00H. Writing indirectly results in no operation.

The memory pointer register MP (01H) is a 7-bit register.

The bit 7 of MP is undefined and reading will return the

result ²1². Any writing operation to MP will only transfer

the lower 7-bit data to MP.

Accumulator

The accumulator closely relates to ALU operations. It is

also mapped to location 05H of the data memory and is

capable of carrying out immediate data operations. Data

movement between two data memory locations has to

pass through the accumulator.

Arithmetic and Logic Unit - ALU

This circuit performs 8-bit arithmetic and logic operation.

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 contents of the status register.

Status Register - STATUS

This 8-bit status register (0AH) contains the zero flag

(Z), carry flag (C), auxiliary carry flag (AC), overflow flag

(OV), power down flag (PDF) and watchdog time-out

flag (TO). It also records the status information and con-

trols the operation sequence.

With the exception of the TO and PDF flags, bits in the

status register can be altered by instructions like most

other register. Any data written into the status register

will not change the TO or PDF flags. In addition it should

be noted that operations related to the status register

may give different results from those intended. The TO

and PDF flags can only be changed by the Watchdog

Timer overflow, chip power-up, clearing the Watchdog

Timer and executing the HALT instruction.

The Z, OV, AC and C flags generally reflect the status of

the latest operations.

In addition, on executing the subroutine call, the status

register will not be automatically pushed onto the stack.

If the contents of the status are important and if the sub-

routine can corrupt the status register, precautions must

be taken to save it properly.

Rev. 1.40

6

December 21, 2005

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