HT48R10A datasheet(6/42 Pages) HOLTEK

6 / 42 page

HT48R10A-1

Rev. 1.20

July 2, 2001

Functional Description

Execution flow

The system clock for the microcontroller is de-

rived from either a crystal or an RC oscillator.

The system clock is internally divided into four

non-overlapping clocks. One instruction cycle

consists of four system clock cycles.

Instruction fetching and execution are

pipelined in such a way that a fetch takes an in-

struction cycle while decoding and execution

takes the next instruction cycle. However, the

pipelining scheme causes each instruction to ef-

fectively execute in a cycle. If an instruction

changes the program counter, two cycles are re-

quired to complete the instruction.

Program counter - PC

The program counter (PC) controls the se-

quence in which the instructions stored in pro-

gram ROM are executed and its contents

specify full range of program memory.

After accessing a program memory word to fetch

an instruction code, the contents of the program

counter are incremented by one. The program

counter then points to the memory word contain-

ing the next instruction code.

When executing a jump instruction, conditional

skip execution, loading PCL register, subrou-

tine call, or return from subroutine initial reset,

internal interrupt, external interrupt or return

from interrupt, the PC manipulates the pro-

gram transfer by loading the address corre-

sponding to each instruction.

The conditional skip is activated by instruc-

tions. Once the condition is met, the next in-

struction, fetched during the current

instruction execution, is discarded and a

dummy cycle replaces it to get the proper in-

struction. Otherwise proceed with the next in-

struction.

The lower byte of the program counter (PCL) is

a readable and writable register (06H). Moving

data into the PCL performs a short jump. The

destination will be within the current program

ROM page.

When a control transfer takes place, an addi-

tional dummy cycle is required.

Program memory - ROM

The program memory is used to store the pro-

gram instructions which are to be executed. It

also contains data, table, and interrupt entries,

and is organized into 1024´14 bits, addressed

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 program initializa-

tion. After chip reset, the program always be-

gins execution at location 000H.

· Location 004H

This area is reserved for the external inter-

rupt service program. If the INT input pin is

activated, the interrupt is enabled and the

stack is not full, the program begins execution

at location 004H.

F e tc h IN S T ( P C )

E x ec ut e I N S T ( P C - 1 )

F e tc h IN S T ( P C + 1 )

E x ec ut e I N S T ( P C )

F e tc h IN S T ( P C + 2 )

E x ec ut e I N S T ( P C + 1 )

PC + 1

PC + 2

S yst e m C l o ck

O S C2 ( RC o n l y )

Execution flow

HT48R10A Scheda tecnica(PDF) 6 Page - Holtek Semiconductor Inc

HT48R10A Scheda tecnica(HTML) 6 Page - Holtek Semiconductor Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Scheda tecnica Scarica

Link URL