PIC16F84A-10SLASHSS datasheet(19/124 Pages) MICROCHIP

19 / 124 page

PIC16F8X

DS30430C-page 19

4.5

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). This is indirect addressing.

EXAMPLE 4-1:

INDIRECT ADDRESSING

• Register ﬁle 05 contains the value 10h

• Register ﬁle 06 contains the value 0Ah

• Load the value 05 into the FSR register

• A read of the INDF register will return the value of

10h

• Increment the value of the FSR register by one

(FSR = 06)

• A read of the INDF register now will return the

value of 0Ah.

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 4-2.

EXAMPLE 4-2:

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 4-1. However, IRP is not used in the

PIC16F8X.

FIGURE 4-1:

DIRECT/INDIRECT ADDRESSING

Direct Addressing

RP1 RP0

from opcode

IRP

(FSR)

Indirect Addressing

bank select

location select

bank select

location select

00h

7Fh

00h

0Bh

0Ch

2Fh (1)

30h (1)

7Fh

not used

Bank 0

Bank 1

Bank 2

Bank 3

Note 1:

PIC16F83 and PIC16CR83 devices.

PIC16F84 and PIC16CR84 devices

For memory map detail see Figure 4-1.

4Fh (2)

50h (2)

Addresses

map back

to Bank 0

Data

Memory (3)

not used

PIC16F84A-10/SS Datasheet(PDF) 19 Page - Microchip Technology

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