PIC12C671T-04E/JW 데이터 시트보기 (PDF) - Microchip Technology

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PIC12C671T-04E/JW

8-Pin, 8-Bit CMOS Microcontroller with A/D Converter and EEPROM Data Memory

Microchip Technology 

4.5 Indirect Addressing, INDF and FSR

Registers

The INDF Register is not a physical register. Address-

ing the INDF Register will cause indirect addressing.

Any instruction using the INDF register actually

accesses the register pointed to by the File Select Reg-

ister, FSR. Reading the INDF Register itself indirectly

(FSR = ’0’) will read 00h. Writing to the INDF Register

indirectly results in a no-operation (although status bits

may be affected). An effective 9-bit address is obtained

by concatenating the 8-bit FSR Register and the IRP bit

(STATUS<7>), as shown in Figure 4-4. However, IRP is

not used in the PIC12C67X.

A simple program to clear RAM locations 20h-2Fh

using indirect addressing is shown in Example 4-1.

PIC12C67X

EXAMPLE 4-1: INDIRECT ADDRESSING

movlw

movwf

NEXT

clrf

incf

btfss

goto

CONTINUE

:

0x20

FSR

INDF

FSR,F

FSR,4

NEXT

;initialize pointer

;to RAM

;clear INDF register

;inc pointer

;all done?

;no clear next

;yes continue

FIGURE 4-4: DIRECT/INDIRECT ADDRESSING

Direct Addressing

RP1 RP0(1) 6

from opcode

0

Indirect Addressing

IRP(1) 7

FSR register

0

bank select location select

00

01

00h

bank select

10

11

180h

location select

Data

Memory

not used

7Fh

Bank 0

Bank 1 Bank 2

1FFh

Bank 3

For register file map detail see Figure 4-2.

Note 1: The RP1 and IRP bits are reserved; always maintain these bits clear.

© 1999 Microchip Technology Inc.

DS30561B-page 23

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