FS9912

Rev. 3.6

15/34

11.1.3 Data Memory Organization

The data memory is partitioned into three parts. The address 00h~07h areas are system special registers, like

indirect address, indirect address pointer, status register, working register, interrupt flag, interrupt control

register. The address 08h~7Fh areas are peripheral special registers, like I/O ports, timer, ADC, signal

conditional network control register, LCD driver… .The address 80h~FFh areas are general data memory.

IND0, IND1: indirect addressing mode address

FSR0, FSR1: indirect addressing mode point

PD: Power Down Flag. Cleared by writing 0 or power-on reset. Set by sleep instruction

TO: Watch Dog Time Out Flag. Cleared by writing 0 or power-on reset. Set by Watch Dog Time Out

C: Carry Flag

Z: Zero Flag

E0IF, E0IE: PT1.0 external interrupt flag and enable.

E1IF, E1IE: PT1.1 external interrupt flag and enable.

ADIF, ADIE: Analog to digital converter interrupt flag and enable.

PCIF, PCIE: Program counter interrupt flag and enable.

TMIF, TMIE: 8-bit Timer interrupt flag and enable.

GIE: Global interrupt enable.

11.1.4 System Special Register Description

11.1.4.1

Indirect Addressing IND0 and FSR0 Register

The IND0 register is not a physical register. Addressing the IND0 (00h) will cause an indirect addressing. Any

instruction using the IND0 register actually accesses data pointed to by the FSR0 register.

A simple program to clear RAM 80h-FFh using indirect addressing is shown in following:

MOVLW 080h

MOVWF FSR0

NEXT: CLRF IND0

INCFSZ FSR0, 1

GOTO NEXT

11.1.4.2

Status Register

C： bit 1 R/W Carry Flag or (~Borrow).

Z： bit 0 R/W Zero Flag, set if ALU operation is zero. Reset otherwise.

Two simple examples to illustrate the relation between carry flag and arithmetic instructions.

Example 1

M (80h) = 3Fh M (81h) = F0h WORK = 99h

ADDWF 80h, 1

; 3Fh+99h=D8h DC=1, C=0, Z=0

ADDWF 81h, 1

; F0h+99h=89h DC=0, C=1, Z=0

SUBWF 80h, 1

; 3Fh-99h=A6hDC=1, C=0, Z=0

SUBWF 81h, 1

; F0h-99h=57h DC=0, C=1, Z=0

Name

Address

Content

IND0

00h

Uses contents of FSR0 to address data memory

IND1

01h

Uses contents of FSR1 to address data memory

FSR0

02h

Indirect data memory, address point 0

FSR1

03h

Indirect data memory, address point 1

STATUS 04h

PD

TO

C

Z

WORK

05h

WORK register

INTF

06h

TMIF

PCIF

ADIF

E1IF

E0IF

INTE

07h

GIE

TMIE

PCIE

ADIE

E1IE

E0IE

08h~7Fh

Peripheral special registers

80h~FFh

General data Memory