PIC16F506T-ESLASHMCSQTP datasheet(26/116 Pages) MICROCHIP

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PIC12F510/16F506

DS41268C-page 24

Preliminary

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.

4.8.1

INDIRECT ADDRESSING EXAMPLE

• 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 conjunc-

tion 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 4-5:

DIRECT/INDIRECT ADDRESSING (PIC12F510)

PIC16F506 – Uses FSR<6:5>. Selects from Bank 0 to

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

PIC12F510 – Uses FSR<5>. Selects from Bank 0 to

Bank 1. FSR<7:6> are unimplemented, read as ‘11’.

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 4-2.

bank

select

location select

bank select

Indirect Addressing

Direct Addressing

Data

Memory(1)

0Fh

10h

Bank 0

Bank 1

(FSR)

00h

1Fh

3Fh

(opcode)

(FSR)

Addresses map back to

addresses in Bank 0.

321

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