PIC16F87XA
A simple program to clear RAM locations 20h-2Fh
using indirect addressing is shown in Example 2-2.
2.5
Indirect Addressing, INDF and
FSR Registers
The INDF register is not a physical register. Addressing
the INDF register will cause indirect addressing.
EXAMPLE 2-2:
INDIRECT ADDRESSING
MOVLW 0x20
MOVWF FSR
;initialize pointer
;to RAM
;clear INDF register
;inc pointer
;all done?
;no clear next
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 2-6.
NEXT
CLRF INDF
INCF FSR,F
BTFSS FSR,4
GOTO NEXT
CONTINUE
:
;yes continue
FIGURE 2-6:
DIRECT/INDIRECT ADDRESSING
Direct Addressing
From Opcode
Indirect Addressing
7
RP1:RP0
6
0
0
IRP
FSR register
Bank Select
Location Select
Bank Select Location Select
00
01
80h
10
100h
11
00h
180h
Data
Memory
(1)
7Fh
Bank 0
FFh
Bank 1
17Fh
Bank 2
1FFh
Bank 3
Note 1: For register file map detail, see Figure 2-3.
2001 Microchip Technology Inc.
Advance Information
DS39582A-page 29
MICROCHIP [ MICROCHIP ]
