PIC16LC72A-10E/SS 查看數據表（PDF） - Microchip Technology

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PIC16LC72A-10E/SS

28-Pin 8-Bit CMOS Microcontrollers

Microchip Technology 

PIC16C62B/72A

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).

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 2-1.

EXAMPLE 2-1: 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 2-3. However, IRP is not used in the

PIC16C62B/72A.

FIGURE 2-3: DIRECT/INDIRECT ADDRESSING

RP1:RP0

(1)

Direct Addressing

6

from opcode

0

bank select location select

00

00h

01

80h

10

100h

Indirect Addressing

IRP

7

(1)

FSR register

0

11

180h

bank select

location select

Data

Memory

not used

(2)

(2)

7Fh

FFh

17Fh

1FFh

Bank 0 Bank 1 Bank 2 Bank 3

Note 1: Maintain clear for upward compatibility with future products.

2: Not implemented.

DS35008B-page 18

Preliminary

© 1999 Microchip Technology Inc.

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