PIC16C711-04/P【PDF 95/177 页】IC MCU OTP 1KX14 A/D 18DIP

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PIC16C71X

DS30272A-page 24

1997 Microchip Technology Inc.

Example 4-1 shows the calling of a subroutine in

page 1 of the program memory. This example assumes

that PCLATH is saved and restored by the interrupt ser-

vice routine (if interrupts are used).

EXAMPLE 4-1:

CALL OF A SUBROUTINE IN

PAGE 1 FROM PAGE 0

ORG 0x500

BSF

PCLATH,3

;Select page 1 (800h-FFFh)

BCF

PCLATH,4

;Only on >4K devices

CALL

SUB1_P1

;Call subroutine in

;page 1 (800h-FFFh)

ORG 0x900

SUB1_P1:

;called subroutine

;page 1 (800h-FFFh)

RETURN

;return to Call subroutine

;in page 0 (000h-7FFh)

4.5

Indirect Addressing, INDF and FSR

Registers

The INDF register is not a physical register. Addressing

the INDF register will cause indirect addressing.

Indirect addressing is possible by using the INDF reg-

ister. 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 4-15. However, IRP

is not used in the PIC16C71X devices.

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

using indirect addressing is shown in Example 4-2.

EXAMPLE 4-2:

INDIRECT ADDRESSING

movlw

0x20

;initialize pointer

movwf

FSR

;to RAM

clrf

INDF

;clear INDF register

incf

FSR,F

;inc pointer

btfss

FSR,4

;all done?

goto

;no clear next

CONTINUE

;yes continue

FIGURE 4-15:

DIRECT/INDIRECT ADDRESSING

For register le map detail see Figure 4-4.

Note 1:

The RP1 and IRP bits are reserved, always maintain these bits clear.

Data

Memory

Indirect Addressing

Direct Addressing

bank select

location select

RP1:RP0

from opcode

IRP(1)

FSR register

bank select

location select

Bank 0

Bank 1

Bank 2

Bank 3

FFh

80h

7Fh

00h

17Fh

100h

1FFh

180h

Not

Used

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