PIC16LC72-02/JW 查看數據表（PDF） - Microchip Technology

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PIC16LC72-02/JW

8-Bit CMOS microcontroller with A,D converter

Microchip Technology 

PIC16C72 Series

2.5 Indirect Addressing, INDF and FSR

Registers

The INDF register is not a physical register. Address-

ing 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).

FIGURE 2-11: DIRECT/INDIRECT ADDRESSING

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

NEXT

CONTINUE

movlw

movwf

clrf

incf

btfss

goto

:

0x20 ;initialize pointer

FSR ; to RAM

INDF ;clear INDF register

FSR ;inc pointer

FSR,4 ;all done?

NEXT ;NO, clear next

;YES, continue

An effective 9-bit address is obtained by concatenating

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

shown in Figure 2-11. However, IRP is not used in the

PIC16C72 Series.

RP1:RP0

(2)

Direct Addressing

6

from opcode

0

bank select location select

00

00h

01

80h

10

100h

Indirect Addressing

IRP

7

(2)

FSR register

0

11

180h

bank select

location select

Data

Memory(1)

not used

(3)

(3)

7Fh

FFh

17Fh

1FFh

Bank 0 Bank 1 Bank 2 Bank 3

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

2: Maintain RP1 and IRP as clear for upward compatibility with future products.

3: Not implemented.

© 1998 Microchip Technology Inc.

Preliminary

DS39016A-page 17

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