PIC16F872_06 Datasheet, PDF (23/168 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS Flash Microcontroller with 10-Bit A/D

PIC16F872
2.5 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 2-4.
A simple program to clear RAM locations 20h-2Fh
using indirect addressing is shown in Example 2-1.
EXAMPLE 2-1: INDIRECT ADDRESSING
MOVLW 0x20
MOVWF FSR
NEXT
CLRF INDF
INCF FSR,F
BTFSS FSR,4
GOTO NEXT
CONTINUE
:
;initialize pointer
;to RAM
;clear INDF register
;inc pointer
;all done?
;no clear next
;yes continue
FIGURE 2-4:
DIRECT/INDIRECT ADDRESSING
Direct Addressing
RP1:RP0 6
From Opcode ₀
Indirect Addressing
IRP
7
FSR Register 0
Bank Select Location Select
00
00h
01
80h
10
100h
11
180h
Bank Select
Location Select
Data
Memory⁽¹⁾
7Fh
FFh
17Fh
1FFh
Bank 0 Bank 1 Bank 2 Bank 3
Note 1: For register file map detail, see Figure 2-2.
© 2006 Microchip Technology Inc.
DS30221C-page 21