PIC12F508_09 datasheet(28/110 Pages) MICROCHIP

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PIC12F508/509/16F505

DS41236E-page 28

4.9

Indirect Data Addressing: INDF

and FSR Registers

The INDF register

not

a physical

Addressing INDF actually addresses the register

whose address is contained in the FSR register (FSR

is a pointer). This is indirect addressing.

4.9.1

INDIRECT ADDRESSING

• Register file 07 contains the value 10h

• Register file 08 contains the value 0Ah

• Load the value 07 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 = 08)

• A read of the INDR 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 10h-1Fh

using indirect addressing is shown in Example 4-1.

EXAMPLE 4-1:

HOW TO CLEAR RAM

USING INDIRECT

ADDRESSING

The FSR is a 5-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.

FIGURE 4-7:

DIRECT/INDIRECT ADDRESSING (PIC12F508/509)

PIC12F508 – Does not use banking. FSR <7:5> are

unimplemented and read as ‘1’s.

PIC12F509 – Uses FSR<5>. Selects between bank 0

and bank 1. FSR<7:6> are unimplemented, read as

‘1’.

PIC16F505 – Uses FSR<6:5>. Selects from bank 0 to

bank 3. FSR<7> is unimplemented, read as ‘1’.

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 Section 4.3 “Data Memory Organization”.

PIC12F509.

Bank

Location Select

Bank Select

Indirect Addressing

Direct Addressing

Data

Memory(1)

0Fh

10h

Bank 0

Bank 1(2)

(FSR)

00h

1Fh

3Fh

(opcode)

(FSR)

Addresses

map back to

addresses

in Bank 0.

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