PIC16F877ATISLASHML datasheet(33/234 Pages) MICROCHIP

33 / 234 page

 2003 Microchip Technology Inc.

DS39582B-page 31

PIC16F87XA

2.5

Indirect Addressing, INDF and

FSR Registers

The INDF register is not a physical register. Addressing

the INDF register will cause indirect addressing.

Indirect addressing is possible by using the INDF reg-

ister. Any instruction using the INDF register actually

accesses the register pointed to by the File Select Reg-

ister, FSR. Reading the INDF register itself, indirectly

(FSR = 0) will read 00h. Writing to the INDF register

indirectly results in a no operation (although status bits

may be affected). An effective 9-bit address is obtained

by concatenating the 8-bit FSR register and the IRP bit

(Status<7>) as shown in Figure 2-6.

A simple program to clear RAM locations 20h-2Fh

using indirect addressing is shown in Example 2-2.

EXAMPLE 2-2:

INDIRECT ADDRESSING

FIGURE 2-6:

DIRECT/INDIRECT ADDRESSING

MOVLW 0x20

;initialize pointer

MOVWF FSR

;to RAM

CLRF

INDF

;clear INDF register

INCF

FSR,F

;inc pointer

BTFSS FSR,4

;all done?

GOTO

;no clear next

CONTINUE

;yes continue

Note 1: For register file map detail, see Figure 2-3.

Data

Memory(1)

Indirect Addressing

Direct Addressing

Bank Select

Location Select

RP1:RP0

From Opcode

IRP

FSR Register

Bank Select

Location Select

Bank 0

Bank 1

Bank 2

Bank 3

FFh

80h

7Fh

00h

17Fh

100h

1FFh

180h

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