12F629 datasheet(20/136 Pages) MICROCHIP

20 / 136 page

PIC12F629/675

DS41190G-page 20

 2010 Microchip Technology Inc.

2.4

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

actually accesses data pointed to by the File Select

produce 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 2-2.

A simple program to clear RAM location 20h-2Fh using

indirect addressing is shown in Example 2-1.

EXAMPLE 2-1:

INDIRECT ADDRESSING

FIGURE 2-2:

DIRECT/INDIRECT ADDRESSING PIC12F629/675

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

For memory map detail see Figure 2-2.

Note 1: The RP1 and IRP bits are reserved; always maintain these bits clear.

Data

Memory

Indirect Addressing

Direct Addressing

Bank Select Location Select

RP1(1) RP0

From Opcode

IRP(1)

FSR Register

Bank Select

Location Select

180h

1FFh

00h

7Fh

Bank 0

Bank 1

Bank 2

Bank 3

Not Used

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