PIC16LC62B datasheet(18/120 Pages) MICROCHIP

18 / 120 page

PIC16C62B/72A

DS35008B-page 18

Preliminary

2.5

Indirect Addressing, INDF and FSR

Registers

The INDF register is not a physical register. Address-

ing INDF actually addresses the register whose

address is contained in the FSR register (FSR is a

pointer).

Reading INDF itself indirectly (FSR = 0) will produce

00h. Writing to the INDF register indirectly results in a

no-operation (although STATUS bits may be affected).

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

using indirect addressing is shown in Example 2-1.

EXAMPLE 2-1:

HOW TO CLEAR RAM

USING INDIRECT

ADDRESSING

movlw

0x20

;initialize pointer

movwf

FSR

;

to RAM

clrf

INDF

;clear INDF register

incf

FSR

;inc pointer

btfss

FSR,4 ;all done?

goto

;NO, clear next

CONTINUE

;YES, continue

An effective 9-bit address is obtained by concatenating

the 8-bit FSR register and the IRP bit (STATUS<7>), as

shown in Figure 2-3. However, IRP is not used in the

PIC16C62B/72A.

FIGURE 2-3:

DIRECT/INDIRECT ADDRESSING

Note 1: Maintain clear for upward compatibility with future products.

2: Not implemented.

Data

Memory

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

not used

FFh

80h

7Fh

00h

17Fh

100h

1FFh

180h

(1)

(2)

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