PIC16C925T-SSLASHCL datasheet(28/182 Pages) MICROCHIP

28 / 182 page

PIC16C925/926

DS39544A-page 26

Preliminary

 2001 Microchip Technology Inc.

2.6

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 produce 00h. Writing to the INDF regis-

ter 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: For memory map detail, see Figure 2-3.

Data

Memory

Indirect Addressing

Direct Addressing

Bank Select

Location Select

RP1:RP0

From Opcode

IRP

FSR Register

Bank Select

Location Select

00h

7Fh

00h

7Fh

Bank 0

Bank 1

Bank 2

Bank 3

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