Datasheet

PIC16C62B/72A
DS35008C-page 18 Preliminary  1998-2013 Microchip Technology Inc.
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
movlw 0x20 ;initialize pointer
movwf FSR ; to RAM
NEXT clrf INDF ;clear INDF register
incf FSR ;inc pointer
btfss FSR,4 ;all done?
goto NEXT ;NO, clear next
CONTINUE
: ;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
Note 1: Maintain clear for upward compatibility with future products.
2: Not implemented.
Data
Memory
Indirect AddressingDirect Addressing
bank select location select
RP1:RP0 6
0
from opcode
IRP FSR register
7
0
bank select
location select
00 01 10 11
Bank 0 Bank 1 Bank 2 Bank 3
not used
FFh
80h
7Fh
00h
17Fh
100h
1FFh
180h
(1)
(1)
(2) (2)