GMS81C50 Datasheet, PDF(27/99 Page) Hynix Semiconductor – 8-BIT SINGLE CHIP MICROCONTROLLERS

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GMS81C50 Datasheet, PDF (27/99 Pages) Hynix Semiconductor – 8-BIT SINGLE CHIP MICROCONTROLLERS

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GMS81C50 Series

HYUNDAI

8.2 Program Memory

A 16-bit program counter is capable of addressing up to

64K bytes, but this device has 16K/24K/32K bytes pro-

gram memory space only physically implemented. Ac-

cessing a location above FFFFH will cause a wrap-around

to 0000H.

Figure 8-5 , shows a map of Program Memory. After reset,

the CPU begins execution from reset vector which is stored

in address FFFEH and FFFFH as shown in Figure 8-6 .

As shown in Figure 8-5 , each area is assigned a fixed lo-

cation in Program Memory. Program Memory area con-

tains the user program.

8000H

A000H

32KByte

Range

24KByte

Range

C000H

16KByte

Range

FF00H

FFC0H

FFE0H

FFFFH

PCALL

AREA

TCALL

AREA

INTERRUPT

VECTOR AREA

PROGRAM

MEMORY

U-PAGE

Figure 8-5 Program Memory Map

Page Call (PCALL) area contains subroutine program to

reduce program byte length by using 2 bytes PCALL in-

stead of 3 bytes CALL instruction. If it is frequently

called, it is more useful to save program byte length.

Table Call (TCALL) causes the CPU to jump to each

TCALL address, where it commences the execution of the

service routine. The Table Call service area spaces 2-byte

for every TCALL: 0FFC0H for TCALL15, 0FFC2H for

TCALL14, etc., as shown in Figure 8-7 .

Example: Usage of TCALL

LDA

TCALL 0FH

;

;TABLE CALL ROUTINE

;

FUNC_A: LDA LRG0

RET

;

FUNC_B: LDA LRG1 2

RET

;

;TABLE CALL ADD. AREA

;

ORG 0FFC0H

DW FUNC_A

DW FUNC_B

;1BYTE INSTR UCTIO N

;INSTEAD OF 2 BYTES

;NOR M AL C ALL

;TCALL ADDRESS AREA

The interrupt causes the CPU to jump to specific location,

where it commences the execution of the service routine.

The External interrupt 0, for example, is assigned to loca-

tion 0FFFAH. The interrupt service locations spaces 2-byte

interval: 0FFF8H and 0FFF9H for External Interrupt 1,

0FFFAH and 0FFFBH for External Interrupt 0, etc.

Any area from 0FF00H to 0FFFFH, if it is not going to be

used, its service location is available as general purpose

Program Memory.

Address

0FFDEH

Vector Area Memory

S/W Interrupt Vector Area

Basic Interval Timer Interrupt Vector Area

Watch Dog Timer Interrupt Vector Area

Timer2 Interrupt Vector Area

Timer1 Interrupt Vector Area

Timer0 Interrupt Vector Area

External Interrupt 2 Vector Area

External Interrupt 1 Vector Area

Key Scan Interrupt Vector Area

RESET Vector Area

NOTE:

"-" means reserved area.

Figure 8-6 Interrupt Vector Area

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