PIC16F526-ISLASHP datasheet(22/122 Pages) MICROCHIP

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PIC16F526

DS41326D-page 22

 2010 Microchip Technology Inc.

4.8

Indirect Data Addressing: INDF

and FSR Registers

The INDF Register is not a physical register.

Addressing INDF actually addresses the register

whose address is contained in the FSR Register (FSR

is a pointer). This is indirect addressing.

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).

The FSR is an 8-bit wide register. It is used in

conjunction with the INDF Register to indirectly

address the data memory area.

The FSR<4:0> bits are used to select data memory

addresses 00h to 1Fh.

FSR<6:5> are the bank select bits and are used to

select the bank to be addressed (00 = Bank 0,

01 =Bank 1, 10 = Bank 2, 11 = Bank 3).

FSR<7> is unimplemented and read as ‘1’.

A simple program to clear RAM locations 10h-1Fh

using indirect addressing is shown in Example 4-1.

EXAMPLE 4-1:

HOW TO CLEAR RAM

USING INDIRECT

ADDRESSING

FIGURE 4-4:

DIRECT/INDIRECT ADDRESSING

MOVLW

0x10

;initialize pointer

MOVWF

FSR

;to RAM

CLRF

INDF

;clear INDF

;register

INCF

FSR,F

;inc pointer

BTFSC

FSR,4

;all done?

GOTO

;NO, clear next

CONTINUE

;YES, continue

Note 1: For register map detail see Figure 4-1.

bank

select

location select

bank select

Indirect Addressing

Direct Addressing

Data

Memory(1)

0Ch

0Dh

(FSR)

00h

0Fh

2Fh

4Fh

6Fh

(opcode)

(FSR)

Addresses map back to

addresses in Bank 0.

10h

Bank 0

Bank 1

Bank 2

Bank 3

1Fh

3Fh

5Fh

7Fh

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