Datasheet

PIC16C77X
 1999-2013 Microchip Technology Inc. Advance Information DS30275B-page 25
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 ). This is indirect addressing.
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 2-11.
FIGURE 2-11: DIRECT/INDIRECT ADDRESSING
Note 1: For register file map detail see Figure 2-2.
Data
Memory(1)
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
FFh
80h
7Fh
00h
17Fh
100h
1FFh
180h
774.book Page 25 Tuesday, January 29, 2013 12:02 PM