Datasheet
1997-2013 Microchip Technology Inc. Preliminary DS30453E-page 33
PIC16C5X
6.7 Indirect Data Addressing; INDF
and FSR Registers
The INDF Register is not a physical register.
Addressing INDF actually addresses the register
whose address is contained in the FSR Register (FSR
is a pointer). This is indirect addressing.
EXAMPLE 6-1: INDIRECT ADDRESSING
• Register file 08 contains the value 10h
• Register file 09 contains the value 0Ah
• Load the value 08 into the FSR Register
• A read of the INDF Register will return the value
of 10h
• Increment the value of the FSR Register by one
(FSR = 09h)
• A read of the INDF register now will return the
value of 0Ah.
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 10h-1Fh
using indirect addressing is shown in Example 6-2.
EXAMPLE 6-2: HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
MOVLW H'10' ;initialize pointer
MOVWF FSR ; to RAM
NEXT CLRF INDF ;clear INDF Register
INCF FSR,F ;inc pointer
BTFSC FSR,4 ;all done?
GOTO NEXT ;NO, clear next
CONTINUE
: ;YES, continue
The FSR is either a 5-bit (PIC16C54, PIC16CR54,
PIC16C55, PIC16C56, PIC16CR56) or 7-bit
(PIC16C57, PIC16CR57, PIC16C58, PIC16CR58)
wide register. It is used in conjunction with the INDF
Register to indirectly address the data memory area.
The FSR<4:0> bits are used to select data memory
addresses 00h to 1Fh.
PIC16C54, PIC16CR54, PIC16C55, PIC16C56,
PIC16CR56: These do not use banking. FSR<6:5> bits
are unimplemented and read as '1's.
PIC16C57, PIC16CR57, PIC16C58, PIC16CR58:
FSR<6:5> are the bank select bits and are used to
select the bank to be addressed (00 = bank 0,
01 =bank 1, 10 = bank 2, 11 = bank 3).
FIGURE 6-10: DIRECT/INDIRECT ADDRESSING
Note 1: For register map detail see Section 6.2.
bank
location select
location select
bank select
Indirect Addressing
Direct Addressing
Data
Memory
(1)
0Fh
10h
Bank 0 Bank 1 Bank 2 Bank 3
0
4
5
6
(FSR)
1000 01 11
00h
1Fh 3Fh 5Fh 7Fh
(opcode)
04
5
6
(FSR)
Addresses map back to
addresses in Bank 0.
3
2
1
3
2
1