HT48RA0 datasheet(4/32 Pages) HOLTEK

4 / 32 page

HT48RA0-2/HT48CA0-2

Rev. 1.50

July 23, 2004

Program Counter

- PC

The 10-bit program counter (PC) controls the sequence

in which the instructions stored in program ROM are ex-

ecuted and its contents specify a maximum of 1024 ad-

dresses.

After accessing a program memory word to fetch an in-

struction code, the contents of the program counter are

incremented by one. The program counter then points to

the memory word containing the next instruction code.

When executing a jump instruction, conditional skip ex-

ecution, loading PCL register, subroutine call, initial re-

set or return from subroutine, the PC manipulates the

program transfer by loading the address corresponding

to each instruction.

The conditional skip is activated by instruction. Once the

condition is met, the next instruction, fetched during the

current instruction execution, is discarded and a dummy

cycle replaces it to get the proper instruction. Otherwise

proceed with the next instruction.

The lower byte of the program counter (PCL) is a read-

able and writeable register (06H). Moving data into the

PCL performs a short jump. The destination will be

within 256 locations.

When a control transfer takes place, an additional

dummy cycle is required.

Program Memory

- ROM

The program memory is used to store the program in-

structions which are to be executed. It also contains

data and table and is organized into 1024

´14 bits, ad-

dressed by the program counter and table pointer.

Certain locations in the program memory are reserved

for special usage:

· Location 000H

This area is reserved for the initialization program. Af-

ter chip reset, the program always begins execution at

location 000H.

· Table location

Any location in the EPROM space can be used as

look-up tables. The instructions TABRDC [m] (the cur-

rent page, one page=256 words) and TABRDL [m]

(the last page) transfer the contents of the lower-order

byte to the specified data memory, and the

Mode

Program Counter

Initial reset

0000000000

Skip

PC+2

Loading PCL

Jump, call branch

Return from subroutine

Program Counter

Note:

*9~*0: Program counter bits

S9~S0: Stack register bits

#9~#0: Instruction code bits

@7~@0: PCL bits

0 0 0 H

D e v i c e i n i t i a l i z a t i o n p r o g r a m

P r o g r a m

1 4 b i t s

L o o k - u p t a b l e ( 2 5 6 w o r d s )

n 0 0 H

L o o k - u p t a b l e ( 2 5 6 w o r d s )

3 F F H

N o t e : n r a n g e s f r o m 0 t o 3

n F F H

Program Memory

Instruction(s)

Table Location

TABRDC [m]

TABRDL [m]

Table Location

Note:

*9~*0: Table location bits

@7~@0: Table pointer bits

P9~P8: Current program counter bits

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