PIC16C712 datasheet(20/106 Pages) MICROCHIP

20 / 106 page

PIC16C712/716

DS41106C-page 20

 1999-2013 Microchip Technology Inc.

2.5

Indirect 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.

EXAMPLE 2-1:

INDIRECT ADDRESSING

• Register file 05 contains the value 10h

• Register file 06 contains the value 0Ah

• Load the value 05 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 = 06)

• 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 20h-2Fh

using indirect addressing is shown in Example 2-2.

EXAMPLE 2-2:

HOW TO CLEAR RAM

USING INDIRECT

ADDRESSING

An effective 9-bit address is obtained by concatenating

the 8-bit FSR register and the IRP bit (STATUS<7>), as

shown in Figure 2-10. However, IRP is not used in the

PIC16C712/716.

FIGURE 2-10:

DIRECT/INDIRECT ADDRESSING

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

Note 1: For register file map detail see Figure 2-3.

2: Maintain clear for upward compatibility with future products.

3: Not implemented.

Data

Memory(1)

Indirect Addressing

Direct Addressing

bank select

location select

RP1:RP0

from opcode

IRP

FSR register

bank select

location select

Bank 0

Bank 1

Bank 2

Bank 3

FFh

80h

7Fh

00h

17Fh

100h

1FFh

180h

(3)

(2)

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